Lars H, 2011-04-01: hubs is a package for communication between Tcl processes, that I started writing several years ago, but (so far) haven't gotten around to completing. I'm making the code as-is available however, since one feature — the hubs remote interp — that got finished seems like it could be utilised within a GSoC project.
The main source for hubs is
http://abel.math.umu.se/~lars/tcl/hubs.dtx
and the documentation that exists is
http://abel.math.umu.se/~lars/tcl/hubs.pdf
Hubs remote interp is a wikification of Section 8 of these. Previous sections have more information on specific protocols and interfaces in the system. The wire protocol (how messages are encoded for transmission over a channel) is also explained here on this wiki, in the "Wire Protocol" section of Tool Protocol Language.