The Tcl Developer Xchange (aka TDX) is a site based on the ArsDigita Community System ACS. It can now be reached via the most Tcl-centric URL the web has to offer:
http://www.tcl.tk/
This site is hosted by ActiveState (and was inherited from Scriptics, Ajuba Solutions, Interwoven).
It also contains a resource, which deserves more attention (IMO, JCW):
http://resource.tcl.tk/
Things you will find there are:
Access is open to anyone, adding/maintaining entries requires a simple login so the identity of contributors can be established.
See also Where to store information and programs and places to find Tcl binaries and sources.