diff --git a/syndicate/actor.rkt b/syndicate/actor.rkt
index 0279a93..80103b4 100644
--- a/syndicate/actor.rkt
+++ b/syndicate/actor.rkt
@@ -7,7 +7,10 @@
 
          current-turn
 
-         actor-system
+         make-actor-system
+         make-actor-group
+         actor-system-wait
+         actor-system-shutdown!
 
          actor?
          actor-id
@@ -55,6 +58,10 @@
          turn-sync!*
          turn-message!)
 
+(module+ internals
+  (provide make-actor
+           actor-terminate!))
+
 (require (only-in preserves preserve=?))
 (require racket/match)
 (require (only-in racket/exn exn->string))
@@ -92,7 +99,7 @@
                [exit-hooks #:mutable])
   #:methods gen:custom-write
   [(define (write-proc a port mode)
-     (fprintf port "#<actor:~a:~a>" (actor-id a) (actor-name a)))])
+     (fprintf port "#<actor:~a/~a:~a>" (engine-id (actor-engine a)) (actor-id a) (actor-name a)))])
 
 (struct facet (id
                actor
@@ -158,12 +165,35 @@
 
 ;;--------------------------------------------------------------------------
 
-(define (actor-system boot-proc #:name [name 'actor-system])
-  (define e (make-engine 1))
-  (make-actor name e #t boot-proc (make-hash))
-  (adjust-inhabitant-count! e -1)
+(define (make-actor-system boot-proc #:name [name 'actor-system])
+  (define e (make-engine 1 name (lambda (restart)
+                                  (actor-system-shutdown! e)
+                                  (restart void))))
+  (queue-task! e (lambda ()
+                   (make-actor name e #t boot-proc (make-hash))
+                   (adjust-inhabitant-count! e -1)))
+  (actor-system-wait e))
+
+(define (make-actor-group outer-boot-proc inner-boot-proc #:name [name 'actor-group])
+  (define f (turn-facet! (lambda ()
+                           (facet-prevent-inert-check! (turn-active-facet (current-turn)))
+                           (outer-boot-proc))))
+  (define e (make-engine 1 name (lambda (restart)
+                                  (turn! f (lambda () (turn-stop!)))
+                                  (actor-system-shutdown! e)
+                                  (restart void))))
+  (queue-task! e (lambda ()
+                   (make-actor name e #t inner-boot-proc (make-hash))
+                   (adjust-inhabitant-count! e -1)))
+  e)
+
+(define (actor-system-wait e)
   (thread-wait (engine-thread e)))
 
+(define (actor-system-shutdown! e)
+  (for [(ac (in-list (engine-shutdown! e)))]
+    (actor-terminate! ac #t)))
+
 (define (make-actor name engine daemon? boot-proc initial-assertions)
   (define ac (actor (generate-actor-id)
                     name
@@ -179,6 +209,9 @@
   (log-syndicate/actor-info "~a booting" ac)
   (define user-root-facet (make-facet ac (actor-root ac) initial-assertions))
   (turn! user-root-facet (stop-if-inert-after boot-proc))
+  (if (engine-running? engine)
+      (engine-register! engine ac)
+      (actor-terminate! ac #t))
   user-root-facet)
 
 (define (actor-add-exit-hook! ac hook)
@@ -207,6 +240,7 @@
                    (turn! (actor-root ac)
                           (lambda () (facet-terminate! (actor-root ac) (eq? reason #t)))
                           #t)
+                   (engine-deregister! (actor-engine ac) ac)
                    (when (not (actor-daemon? ac))
                      (adjust-inhabitant-count! (actor-engine ac) -1))))))
 
@@ -334,15 +368,15 @@
 (define (turn-ref turn entity [attenuation '()])
   (entity-ref (turn-active-facet turn) entity attenuation))
 
-(define (turn-facet! turn boot-proc)
-  (let ((new-facet (make-facet (facet-actor (turn-active-facet turn))
-                               (turn-active-facet turn))))
+(define (turn-facet! boot-proc)
+  (define turn (current-turn))
+  (let ((new-facet (make-facet (facet-actor (turn-active-facet turn)) (turn-active-facet turn))))
     (with-active-facet new-facet (stop-if-inert-after boot-proc))
     new-facet))
 
-(define (turn-stop! turn [f (turn-active-facet turn)] [continuation #f])
+(define (turn-stop! [f (turn-active-facet (current-turn))] [continuation #f])
   (log-syndicate/actor-debug "  ENQ stop-facet ~v" f)
-  (turn-enqueue! turn
+  (turn-enqueue! (current-turn)
                  f
                  (lambda ()
                    (log-syndicate/actor-debug "  DEQ stop-facet ~v" f)
@@ -505,7 +539,7 @@
                    (lambda ()
                      (when (or (and (facet-parent f) (not (facet-live? (facet-parent f))))
                                (facet-inert? f))
-                       (turn-stop! (current-turn)))))))
+                       (turn-stop!))))))
 
 (define (deliver maybe-proc . args)
   (when maybe-proc
diff --git a/syndicate/dataspace.rkt b/syndicate/dataspace.rkt
index ecf56e5..d1db868 100644
--- a/syndicate/dataspace.rkt
+++ b/syndicate/dataspace.rkt
@@ -52,7 +52,7 @@
             #:message (lambda (message)
                         (log-syndicate/dataspace-debug "~v ! ~v" ds-e message)
                         (send-assertion! this-turn skeleton message))))
-  ds-e)
+  (ref ds-e))
 
 (define-syntax actor-system/dataspace
   (syntax-rules ()
@@ -60,5 +60,5 @@
      (actor-system
       #:name 'dataspace
       (facet-prevent-inert-check! this-facet)
-      (define ds (ref (dataspace)))
+      (define ds (dataspace))
       expr ...)]))
diff --git a/syndicate/distributed/tcp-server.rkt b/syndicate/distributed/tcp-server.rkt
index 2df4e64..fa0592f 100644
--- a/syndicate/distributed/tcp-server.rkt
+++ b/syndicate/distributed/tcp-server.rkt
@@ -32,7 +32,7 @@
                           #:packet-writer (lambda (bs) (send-data conn bs))
                           #:setup-inputs
                           (lambda (tr)
-                            (accept-connection conn #:on-data (lambda (bs) (accept-bytes tr bs))))
+                            (accept-connection conn #:on-data (lambda (d _m) (accept-bytes tr d))))
                           #:initial-ref
                           (object #:name (list conn 'gatekeeper)
                                   [(Resolve unvalidated-sturdyref observer)
diff --git a/syndicate/drivers/tcp.rkt b/syndicate/drivers/tcp.rkt
index 6bb9a79..57cd962 100644
--- a/syndicate/drivers/tcp.rkt
+++ b/syndicate/drivers/tcp.rkt
@@ -66,8 +66,9 @@
                             (tcp-connect host port)))
      (lambda ()
        (define name (call-with-values (lambda () (tcp-addresses i #t)) list))
-       (on-stop (close-input-port i)
-                (close-output-port o))
+       (actor-add-exit-hook! this-actor (lambda ()
+                                          (close-input-port i)
+                                          (close-output-port o)))
        (define issue-credit (start-inbound-relay connection-custodian name (lambda () local-peer) i))
        (define relay (outbound-relay name o))
        (at local-peer
@@ -81,9 +82,9 @@
   (define name (call-with-values (lambda () (tcp-addresses i #t)) list))
   (spawn
     #:name name
-    (on-stop (close-input-port i)
-             (close-output-port o))
-
+    (actor-add-exit-hook! this-actor (lambda ()
+                                       (close-input-port i)
+                                       (close-output-port o)))
     (define issue-credit #f)
     (define active-controller #f)
     (define relay (outbound-relay name o))
@@ -219,7 +220,13 @@
                      [#:asserted (Socket-credit amount mode) (on-credit amount mode)]
                      [#:asserted (Socket-data data mode) (on-data data mode)]
                      [#:asserted (Socket-eof) (on-eof)]))))
-  (when initial-credit (send-credit conn initial-credit initial-mode)))
+  (when initial-credit (send-credit conn initial-credit initial-mode))
+  (lambda (#:on-data [new-on-data #f]
+           #:on-eof [new-on-eof #f]
+           #:on-credit [new-on-credit #f])
+    (when new-on-data (set! on-data new-on-data))
+    (when new-on-eof (set! on-eof new-on-eof))
+    (when new-on-credit (set! on-credit new-on-credit))))
 
 (define (establish-connection ds spec
                               #:initial-credit [initial-credit (CreditAmount-unbounded)]
diff --git a/syndicate/engine.rkt b/syndicate/engine.rkt
index f7b526b..1b96570 100644
--- a/syndicate/engine.rkt
+++ b/syndicate/engine.rkt
@@ -3,11 +3,18 @@
 ;;; SPDX-FileCopyrightText: Copyright © 2021 Tony Garnock-Jones <tonyg@leastfixedpoint.com>
 
 (provide engine?
+         engine-id
+         engine-name
+         engine-running?
+         engine-custodian
          engine-thread
          engine-inhabitant-count
          make-engine
          adjust-inhabitant-count!
          queue-task!
+         engine-register!
+         engine-deregister!
+         engine-shutdown!
          *dead-engine*)
 
 (require racket/match)
@@ -16,34 +23,41 @@
 
 (define-logger syndicate/engine)
 
-(struct engine (id thread [inhabitant-count #:mutable])
+(struct engine (id name custodian thread [running? #:mutable] actors [inhabitant-count #:mutable])
   #:methods gen:custom-write
   [(define (write-proc e port mode)
-     (fprintf port "#<engine:~a>" (engine-id e)))])
+     (fprintf port "#<engine:~a:~a>" (engine-id e) (engine-name e)))])
 
 (define generate-engine-id (make-counter))
 
-(define (make-engine initial-inhabitant-count)
+(define (make-engine initial-inhabitant-count name termination-handler)
+  (define custodian (make-custodian))
   (define e (engine (generate-engine-id)
-                    (thread (lambda ()
-                              (thread-receive) ;; delay boot until we're ready
-                              (log-syndicate/engine-debug "~a starting" e)
-                              (with-handlers ([exn? (handle-unexpected-task-runner-termination e)])
-                                (let loop ()
-                                  (log-syndicate/engine-debug
-                                   "~a task count: ~a" e (engine-inhabitant-count e))
-                                  (if (positive? (engine-inhabitant-count e))
-                                      ;; We have some non-daemon users so just block
-                                      (begin ((thread-receive))
-                                             (loop))
-                                      ;; No non-daemon users, so keep running until there's no more work
-                                      (match (thread-try-receive)
-                                        [#f ;; No work, no non-daemons, we're done.
-                                         (void)]
-                                        [thunk
-                                         (thunk)
-                                         (loop)])))
-                                (log-syndicate/engine-debug "~a stopping" e))))
+                    name
+                    custodian
+                    (parameterize ((current-custodian custodian))
+                      (thread (lambda ()
+                                (thread-receive) ;; delay boot until we're ready
+                                (log-syndicate/engine-debug "~a starting" e)
+                                (with-handlers ([exn? (handle-unexpected-task-runner-termination e)])
+                                  (let loop ((termination-handler termination-handler))
+                                    (log-syndicate/engine-debug
+                                     "~a task count: ~a" e (engine-inhabitant-count e))
+                                    (if (positive? (engine-inhabitant-count e))
+                                        ;; We have some non-daemon users so just block
+                                        (begin ((thread-receive))
+                                               (loop termination-handler))
+                                        ;; No non-daemon users, so keep running until there's no more work
+                                        (match (thread-try-receive)
+                                          [#f ;; No work, no non-daemons, we're done.
+                                           (termination-handler loop)]
+                                          [thunk
+                                           (thunk)
+                                           (loop termination-handler)])))
+                                  (log-syndicate/engine-debug "~a stopping" e)
+                                  (custodian-shutdown-all custodian)))))
+                    #t
+                    (make-hash)
                     initial-inhabitant-count))
   (thread-send (engine-thread e) 'boot)
   e)
@@ -52,6 +66,23 @@
   (queue-task! e (lambda ()
                    (set-engine-inhabitant-count! e (+ (engine-inhabitant-count e) delta)))))
 
+(define (engine-register! e ac)
+  (when (not (eq? (current-thread) (engine-thread e)))
+    (error 'engine-register! "Called from wrong thread"))
+  (hash-set! (engine-actors e) ac #t))
+
+(define (engine-deregister! e ac)
+  (when (not (eq? (current-thread) (engine-thread e)))
+    (error 'engine-deregister! "Called from wrong thread"))
+  (hash-remove! (engine-actors e) ac))
+
+(define (engine-shutdown! e)
+  (log-syndicate/engine-debug "~a shutdown" e)
+  (set-engine-running?! e #f)
+  (define actors (hash-keys (engine-actors e)))
+  (hash-clear! (engine-actors e))
+  actors)
+
 (define ((handle-unexpected-task-runner-termination e) exn)
   (log-syndicate/engine-error "~a terminated unexpectedly!\n~a" e (exn->string exn))
   (exit 1))
@@ -62,4 +93,4 @@
                (lambda ()
                  (log-syndicate/engine-warning "Attempt to enqueue task for dead engine ~v" e))))
 
-(define *dead-engine* (make-engine 0))
+(define *dead-engine* (make-engine 0 'dead-engine void))
diff --git a/syndicate/main.rkt b/syndicate/main.rkt
index 7e114fd..840caf6 100644
--- a/syndicate/main.rkt
+++ b/syndicate/main.rkt
@@ -14,7 +14,7 @@
 
          :pattern)
 
-(require (except-in "actor.rkt" actor-system))
+(require "actor.rkt")
 (require "entity-ref.rkt")
 (require "syntax.rkt")
 (require preserves)
diff --git a/syndicate/syntax.rkt b/syndicate/syntax.rkt
index 7a6d818..5e55c65 100644
--- a/syndicate/syntax.rkt
+++ b/syndicate/syntax.rkt
@@ -9,6 +9,7 @@
 
          entity
          actor-system
+         actor-group
          object
 
          ref
@@ -46,7 +47,6 @@
 (require preserves-schema)
 
 (require "actor.rkt")
-(require (prefix-in actor: "actor.rkt"))
 (require "entity-ref.rkt")
 
 (require "event-expander.rkt")
@@ -78,7 +78,14 @@
 (define-syntax (actor-system stx)
   (syntax-parse stx
     [(_ name:<name> expr ...)
-     #'(actor:actor-system #:name name.N (lambda () expr ...))]))
+     #'(make-actor-system #:name name.N (lambda () expr ...))]))
+
+(define-syntax (actor-group stx)
+  (syntax-parse stx
+    [(_ name:<name> [outer-facet-expr ...] group-boot-expr ...)
+     #'(make-actor-group #:name name.N
+                         (lambda () outer-facet-expr ...)
+                         (lambda () group-boot-expr ...))]))
 
 (define-syntax (object stx)
   (syntax-parse stx
@@ -158,7 +165,7 @@
   (entity-ref this-facet entity '()))
 
 (define-syntax-rule (react setup-expr ...)
-  (turn-facet! this-turn (lambda () setup-expr ...)))
+  (turn-facet! (lambda () setup-expr ...)))
 
 (define-syntax (let-event stx)
   (syntax-parse stx
@@ -174,8 +181,8 @@
 
 (define-syntax stop-facet
   (syntax-rules ()
-    [(_ f) (turn-stop! this-turn f)]
-    [(_ f expr ...) (turn-stop! this-turn f (lambda () expr ...))]))
+    [(_ f) (turn-stop! f)]
+    [(_ f expr ...) (turn-stop! f (lambda () expr ...))]))
 
 (define-syntax-rule (stop-current-facet expr ...)
   (stop-facet this-facet expr ...))
@@ -277,20 +284,20 @@
 
 (define-event-expander event:when
   (lambda (stx)
-    (syntax-case stx (message asserted retracted)
-      [(_ (message pat) expr ...)
+    (syntax-parse stx
+      [(_ ((~datum message) pat) expr ...)
        #`(assert (Observe (:pattern pat)
                           (ref (entity #:message
                                        (lambda (bindings)
                                          (match-define (list #,@(analyse-pattern-bindings #'pat)) bindings)
                                          expr ...)))))]
-      [(_ (asserted pat) expr ...)
+      [(_ ((~datum asserted) pat) expr ...)
        #`(assert (Observe (:pattern pat)
                           (ref (entity #:assert
                                        (lambda (bindings _handle)
                                          (match-define (list #,@(analyse-pattern-bindings #'pat)) bindings)
                                          expr ...)))))]
-      [(_ (retracted pat) expr ...)
+      [(_ ((~datum retracted) pat) expr ...)
        #`(assert (Observe (:pattern pat)
                           (let ((assertion-map (make-hash)))
                             (ref (entity #:assert
@@ -343,6 +350,7 @@
 
 ;;---------------------------------------------------------------------------
 ;;; Local Variables:
+;;; eval: (put 'actor-group 'racket-indent-function 1)
 ;;; eval: (put 'actor-system/dataspace 'racket-indent-function 1)
 ;;; eval: (put 'at 'racket-indent-function 1)
 ;;; eval: (put 'object 'racket-indent-function 0)