A long-running multi-institutional research project founded in 1989 by Michael Doyle. The various applications developed over the years by the project make heavy use of Tcl/Tk.
The home page for the project workgroup is at http://www.visembryo.org . This site, btw, is running on Mark Roseman's ProjectForum system (http://www.projectforum.com/pf ), which is based on Wikit.