diff --git a/marketplace/examples/debug-chat.rkt b/marketplace/examples/debug-chat.rkt
new file mode 100644
index 0000000..100b925
--- /dev/null
+++ b/marketplace/examples/debug-chat.rkt
@@ -0,0 +1,49 @@
+#lang marketplace
+
+(require "../support/debug.rkt")
+
+(debug
+ (nested-vm
+  #:debug-name 'echo
+  (at-meta-level
+   (endpoint
+    #:subscriber (tcp-channel ? (tcp-listener 5999) ?)
+    #:observer
+    #:conversation (tcp-channel them us _)
+    #:on-presence
+    (debug
+     (spawn #:debug-name (list 'session them)
+	    #:child (chat-session them us)))))))
+
+(define (chat-session them us)
+  (define user (gensym 'user))
+  (transition stateless
+    (listen-to-user user them us)
+    (speak-to-user user them us)))
+
+(define (listen-to-user user them us)
+  (list
+   (endpoint #:publisher `(,user says ,?))
+   (at-meta-level
+    (endpoint #:subscriber (tcp-channel them us ?)
+              #:on-absence (quit)
+              [(tcp-channel _ _ (? bytes? text))
+               (send-message `(,user says ,text))]))))
+
+(define (speak-to-user user them us)
+  (define (say fmt . args)
+    (at-meta-level
+     (send-message
+      (tcp-channel us them (apply format fmt args)))))
+  (define (announce who did-what)
+    (unless (equal? who user)
+      (say "~s ~s.~n" who did-what)))
+  (list
+   (say "You are ~s.~n" user)
+   (at-meta-level
+    (endpoint #:publisher (tcp-channel us them ?)))
+   (endpoint #:subscriber `(,? says ,?)
+     #:conversation `(,who says ,_)
+     #:on-presence (announce who 'arrived)
+     #:on-absence  (announce who 'departed)
+     [`(,who says ,what) (say "~a: ~a" who what)])))
diff --git a/marketplace/support/debug.rkt b/marketplace/support/debug.rkt
index f1b1df4..15cf8a0 100644
--- a/marketplace/support/debug.rkt
+++ b/marketplace/support/debug.rkt
@@ -8,8 +8,14 @@
 (require "../process.rkt")
 (require "../quasiqueue.rkt")
 
+(require/typed "gui.rkt"
+	       [opaque AnyState any-state?]
+	       [open-debugger (Any -> (Values (AnyState -> Void) (-> Void)))])
+
 (provide debug)
 
+(struct: debugger ([out : (AnyState -> Void)] [in : (-> Void)]))
+
 (: debug : (All (ParentState) (Spawn ParentState) -> (Spawn ParentState)))
 (define (debug spawn-child)
   (match-define (core:spawn child-spec parent-k debug-name) spawn-child)
@@ -21,18 +27,25 @@
       (define (wrapped-cotransition k)
 	(: receiver : (All (S) (Transition S) -> R))
 	(define (receiver child-transition)
-	  ((inst k S) (wrap-transition debug-name child-transition)))
+	  (define-values (send-to-debugger! receive-from-debugger!)
+	    (open-debugger debug-name))
+	  (define d (debugger send-to-debugger! receive-from-debugger!))
+	  ((inst k S) (wrap-transition d child-transition)))
 	((inst original-cotransition R) receiver))
       wrapped-cotransition))
    parent-k
    (list 'debug debug-name)))
 
-(: wrap-transition : (All (ChildState) Any (Transition ChildState) -> (Transition ChildState)))
-(define (wrap-transition debug-name child-transition)
+(: wrap-transition : (All (ChildState)
+			  debugger
+			  (Transition ChildState)
+			  -> (Transition ChildState)))
+(define (wrap-transition d child-transition)
+  ((debugger-out d) (cast child-transition AnyState))
+  ((debugger-in d))
   (match-define (core:transition child-state child-actions) child-transition)
-  (log-debug "~v: New State ~v" debug-name child-state)
   (core:transition child-state ((inst action-tree-map ChildState)
-				(wrap-action debug-name)
+				(wrap-action d)
 				child-actions)))
 
 (: action-tree-map : (All (State) ((Action State) -> (Action State))
@@ -43,53 +56,58 @@
    f
    (quasiqueue->list (action-tree->quasiqueue actions))))
 
-(: wrap-action : (All (ChildState) Any -> ((Action ChildState) -> (Action ChildState))))
-(define ((wrap-action debug-name) action)
+(: wrap-action : (All (ChildState)
+		      debugger
+		      -> ((Action ChildState) -> (Action ChildState))))
+(define ((wrap-action d) action)
   (cond
    [(core:yield? action)
-    (log-debug "~v: Yield" debug-name)
-    (core:yield (wrap-interruptk debug-name (core:yield-k action)))]
+    (core:yield (wrap-interruptk d (core:yield-k action)))]
    [(core:at-meta-level? action)
-    (core:at-meta-level (wrap-preaction "Outer" debug-name (core:at-meta-level-preaction action)))]
+    (core:at-meta-level (wrap-preaction #t d (core:at-meta-level-preaction action)))]
    [else
-    (wrap-preaction "Inner" debug-name action)]))
+    (wrap-preaction #f d action)]))
 
-(: wrap-preaction : (All (ChildState) String Any (PreAction ChildState) -> (PreAction ChildState)))
-(define (wrap-preaction level debug-name preaction)
+(: wrap-preaction : (All (ChildState)
+			 Boolean
+			 debugger
+			 (PreAction ChildState)
+			 -> (PreAction ChildState)))
+(define (wrap-preaction meta? d preaction)
   (match preaction
     [(core:add-endpoint pre-eid role handler)
-     (log-debug "~v: ~a AddEndpoint ~v ~v" debug-name level pre-eid role)
-     (core:add-endpoint pre-eid role (wrap-handler debug-name handler))]
+     (core:add-endpoint pre-eid role (wrap-handler meta? d handler))]
     [(core:delete-endpoint pre-eid reason)
-     (log-debug "~v: ~a DeleteEndpoint ~v ~v" debug-name level pre-eid reason)
      preaction]
     [(core:send-message body orientation)
-     (log-debug "~v: ~a SendMessage ~v ~v" debug-name level body orientation)
      preaction]
     [(core:spawn spec maybe-k child-debug-name)
-     (log-debug "~v: ~a Spawn ~v" debug-name level child-debug-name)
-     (core:spawn spec (wrap-spawnk debug-name maybe-k) child-debug-name)]
+     (core:spawn spec (wrap-spawnk d maybe-k) child-debug-name)]
     [(core:quit pid reason)
-     (log-debug "~v: ~a Quit ~v ~v" debug-name level pid reason)
      preaction]))
 
-(: wrap-interruptk : (All (ChildState) Any (InterruptK ChildState) -> (InterruptK ChildState)))
-(define (wrap-interruptk debug-name ik)
+(: wrap-interruptk : (All (ChildState)
+			  debugger
+			  (InterruptK ChildState)
+			  -> (InterruptK ChildState)))
+(define (wrap-interruptk d ik)
   (lambda (state)
-    (log-debug "~v: Old State ~v" debug-name state)
-    (wrap-transition debug-name (ik state))))
+    (wrap-transition d (ik state))))
 
 (: wrap-spawnk : (All (ChildState)
-		      Any
+		      debugger
 		      (Option (PID -> (InterruptK ChildState)))
 		      -> (Option (PID -> (InterruptK ChildState)))))
-(define (wrap-spawnk debug-name maybe-k)
+(define (wrap-spawnk d maybe-k)
   (and maybe-k
-       (lambda: ([child-pid : PID]) (wrap-interruptk debug-name (maybe-k child-pid)))))
+       (lambda: ([child-pid : PID]) (wrap-interruptk d (maybe-k child-pid)))))
 
-(: wrap-handler : (All (ChildState) Any (Handler ChildState) -> (Handler ChildState)))
-(define (wrap-handler debug-name h)
+(: wrap-handler : (All (ChildState)
+		       Boolean
+		       debugger
+		       (Handler ChildState)
+		       -> (Handler ChildState)))
+(define (wrap-handler meta? d h)
   (lambda (event)
-    (log-debug "~v: Incoming Event ~v" debug-name event)
-    (wrap-interruptk debug-name (h event))))
-
+    ((debugger-out d) (cast (cons meta? event) AnyState))
+    (wrap-interruptk d (h event))))
diff --git a/marketplace/support/gui.rkt b/marketplace/support/gui.rkt
new file mode 100644
index 0000000..0d847c5
--- /dev/null
+++ b/marketplace/support/gui.rkt
@@ -0,0 +1,267 @@
+#lang racket/base
+
+(require racket/set)
+(require racket/match)
+(require racket/class)
+(require racket/async-channel)
+(require racket/gui/base)
+(require racket/date)
+(require racket/format)
+(require racket/math)
+
+(require images/icons/control)
+(require images/icons/arrow)
+(require images/icons/symbol)
+(require images/icons/misc)
+(require images/icons/style)
+
+(require racket/pretty)
+
+(require (prefix-in core: "../types.rkt"))
+
+(provide any-state?
+	 open-debugger)
+
+;; Frame
+;;   Toolbar
+;;     Rewind one step - moves without executing
+;;     Fast-forward one step - moves without executing
+;;     --
+;;     Stop
+;;     Run one step
+;;     Play
+;;     --
+;;     Select history depth
+;;     --
+;;     Kill this process
+;;   State display
+;;     If the state is (vm?), special display; permits spawning debuggers on nested processes
+;;   Endpoints display
+;;     Shows ID and role 
+;;     Permits deletion of endpoint
+;;     Permits interaction with endpoint??
+;;   Trace display
+;;     Selection of a row rewinds to that point
+
+(define (any-state? x) #t)
+
+(define (open-debugger name)
+  (define to-debugger (make-channel))
+  (define from-debugger (make-semaphore 0))
+  (parameterize ((current-eventspace (make-eventspace)))
+    (new debugger%
+	 [name name]
+	 [from-vm to-debugger]
+	 [to-vm from-debugger]))
+  (values (lambda (t) (channel-put to-debugger t))
+	  (lambda () (semaphore-wait from-debugger))))
+
+(define debugger%
+  (class object%
+
+    (init-field name)
+    (init-field from-vm)
+    (init-field to-vm)
+
+    (define mutex (make-semaphore 1))
+    (define stepping? #t)
+    (define waiting? #f)
+
+    (define frame (new frame%
+		       [label (format "~a" name)]
+		       [width 480]
+		       [height 700]))
+
+    (define menu-bar (new menu-bar% [parent frame]))
+    (define edit-menu (new menu% [label "Edit"] [parent menu-bar]))
+    (append-editor-operation-menu-items edit-menu #f)
+
+    (define toolbar (new horizontal-pane%
+			 [parent frame]
+			 [stretchable-height #f]
+			 [alignment '(right center)]))
+
+    (define state-panel (new horizontal-panel%
+			     [parent frame]))
+
+    (define endpoints (new list-box%
+			   [style '(single column-headers)]
+			   [label #f]
+			   [choices '()]
+			   [parent frame]
+			   [columns '("ID" "Orientation" "Topic" "Type")]))
+
+    (define events (new list-box%
+			[style '(single column-headers)]
+			[label #f]
+			[choices '()]
+			[parent frame]
+			[columns '("Time" "Dir" "Type" "Detail")]))
+
+    (send endpoints set-column-width 1 32 32 32)
+    (send endpoints set-column-width 3 32 32 32)
+
+    (send events set-column-width 1 32 32 32)
+
+    (define (toolbar-button label [handler void])
+      (new button%
+	   [label label]
+	   [min-width 32]
+	   [parent toolbar]
+	   [callback handler]))
+
+    (define (toolbar-spacer)
+      (new pane% [parent toolbar] [min-width 16] [stretchable-width #f]))
+
+    ;; (toolbar-button (left-over-arrow-icon #:color syntax-icon-color))
+    ;; (toolbar-button (right-over-arrow-icon #:color syntax-icon-color))
+    ;; (toolbar-spacer)
+
+    (define pause-button
+      (toolbar-button (pause-icon #:color halt-icon-color)
+		      (lambda (b e)
+			(send pause-button enable #f)
+			(send play-button enable #t)
+			(send step-button enable #t)
+			(call-with-semaphore
+			 mutex
+			 (lambda ()
+			   (set! stepping? #f))))))
+    (define play-button
+      (toolbar-button (play-icon #:color run-icon-color)
+		      (lambda (b e)
+			(send pause-button enable #t)
+			(send play-button enable #f)
+			(send step-button enable #f)
+			(call-with-semaphore
+			 mutex
+			 (lambda ()
+			   (set! stepping? #t)
+			   (when waiting?
+			     (set! waiting? #f)
+			     (semaphore-post to-vm)))))))
+    (toolbar-spacer)
+    (define step-button
+      (toolbar-button (step-icon #:color run-icon-color)
+		      (lambda (b e)
+			(call-with-semaphore
+			 mutex
+			 (lambda ()
+			   (when waiting?
+			     (set! waiting? #f)
+			     (semaphore-post to-vm)))))))
+
+    (send play-button enable #f)
+    (send step-button enable #f)
+
+    ;; (toolbar-spacer)
+    ;; (toolbar-button "Settings...")
+    ;; (toolbar-spacer)
+    ;; (toolbar-button (stop-sign-icon))
+
+    (define state-text (new text%))
+    (define state-canvas (new editor-canvas%
+			      [parent state-panel]
+			      [editor state-text]
+			      [label "State"]))
+
+    (define controller-thread
+      (thread
+       (lambda ()
+	 (controller-thread-loop))))
+
+    (define (current-timestamp)
+      (define (p n w) (~a (exact-truncate n) #:width w #:align 'right #:pad-string "0"))
+      (define d (current-date))
+      (format "~a:~a:~a.~a ~a-~a-~a"
+	      (p (date-hour d) 2)
+	      (p (date-minute d) 2)
+	      (p (date-second d) 2)
+	      (p (/ (date*-nanosecond d) 1000000.0) 3)
+	      (date-year d)
+	      (p (date-month d) 2)
+	      (p (date-day d) 2)))
+
+    (define (record-event! stamp dir type detail)
+      (define n (send events get-number))
+      (send events append stamp)
+      (send events set-string n dir 1)
+      (send events set-string n type 2)
+      (send events set-string n (~a detail) 3)
+      (send events set-first-visible-item
+	    (max 0 (- n (- (send events number-of-visible-items) 1)))))
+
+    (define (format-action action)
+      (cond
+       [(core:yield? action)
+	(values "Yield" "")]
+       [(core:at-meta-level? action)
+	(format-preaction "Meta" (core:at-meta-level-preaction action))]
+       [else
+	(format-preaction "" action)]))
+
+    (define (format-preaction layer preaction)
+      (define-values (type detail)
+	(match preaction
+	  [(core:add-endpoint pre-eid role handler)
+	   (values "Sub" (string-append (format-role role) " " (~a pre-eid)))]
+	  [(core:delete-endpoint pre-eid reason)
+	   (values "Unsub" (format "~a ~v" pre-eid reason))]
+	  [(core:send-message body 'publisher)
+	   (values "Send" (~v body))]
+	  [(core:send-message body 'subscriber)
+	   (values "Feedback" (~v body))]
+	  [(core:spawn spec maybe-k child-debug-name)
+	   (values "Spawn" (~v child-debug-name))]
+	  [(core:quit #f reason)
+	   (values "Exit" (~v reason))]
+	  [(core:quit pid reason)
+	   (values "Kill" (format "~a ~v" pid reason))]))
+      (values (string-append layer type) detail))
+
+    (define (format-role r)
+      (match-define (core:role orientation topic interest-type) r)
+      (format "~a/~a ~v"
+	      (string-ref (symbol->string orientation) 0)
+	      (string-ref (symbol->string interest-type) 0)
+	      topic))
+
+    (define (handle-from-vm x)
+      (define now (current-timestamp))
+      (match x
+	[(core:transition state actions)
+	 (send state-text erase)
+	 (send state-text insert (pretty-format state))
+	 (let loop ((a actions))
+	   (cond
+	    [(pair? a) (loop (car a)) (loop (cdr a))]
+	    [(or (null? a) (eq? a #f) (void? a)) (void)]
+	    [else (define-values (type detail) (format-action a))
+		  (record-event! now "Act" type detail)]))
+	 (call-with-semaphore
+	  mutex
+	  (lambda ()
+	    (if stepping?
+		(semaphore-post to-vm)
+		(set! waiting? #t))))]
+	[(cons meta? e)
+	 (define prefix (if meta? "Meta" ""))
+	 (match e
+	   [(core:presence-event role)
+	    (record-event! now "Evt" (string-append prefix "Presence") (format-role role))]
+	   [(core:absence-event role reason)
+	    (record-event! now "Evt" (string-append prefix "Absence")
+			   (string-append (format-role role) " " (~v reason)))]
+	   [(core:message-event _ message)
+	    (record-event! now "Evt" (string-append prefix "Recv") (~v message))])]))
+
+    (define (controller-thread-loop)
+      (sync (handle-evt from-vm
+			(lambda (x)
+			  (handle-from-vm x)
+			  (controller-thread-loop)))))
+
+    (super-new)
+
+    (send frame show #t)
+    ))