libace-tkreactor-6.3.3 6.3.3+dfsg-1 (i386 binary) in ubuntu xenial

 Recognizing the need to write reactor-based GUI applications, the ACE
 community has created several reactor extensions for use with X
 Window System. Each of these extends the ACE_Select_Reactor to work
 with a specific toolkit. By using these reactors, your GUI
 application can remain single threaded yet still respond to both GUI
 events, such as button presses, and your own application events.
 .
 The ACE_TkReactor provides reactor functionality around the popular
 Tcl/Tk library. The underlying Tcl/Tk method used is
 Tcl_DoOneEvent().