TkXext "has the ability to send events to any window, embed windows in Tk,
and send events to embedded or non-embedded windows."  Unlike [Android], it doesn't
yet (as of September 2001) have capabilities for dispinfo or
event recording.

[GPS] maintains TkXext at http://www.xmission.com/~georgeps/tkxext/ , with the help
of several others.

TkXext is X-based; it's available only for Unix.

(more accurately, it's available as source, and good luck figuring out how to compile it under windows to work with Exceed [http://www.hummingbird.com/products/nc/exceed/] or Reflections/X... But if you do work it out, by all means let George know about it.)