TIP is the acronym for Tcl Improvement Proposal, a process put into place by the Tcl Core Team (TCT) for submitting changes to Tcl or Tk that would result in C API or script level API interfaces.
The home base for TIPs is http://www.purl.org/tcl/tip/ or http://tip.tcl.tk/ (they end up at the same place after magical behind-the-scenes URL rewriting)
For people who do not feel that they have the technical expertise to see a TIP through the process, at least for Tcl and Tk there is the SourceForge Feature Request mechanism.
Long ago, when "Unix" often as not meant "Solaris" (except that it was called "SunOS" then) or something now regarded as even more recondite, serial port work generally involved the command-line utilities tip(1) and cu(1) ([L1 ], or [L2 ], for example). Questions sometimes still arise about these from new readers of Exploring Expect, because that venerable volume was written at a time when tip(1) constituted a natural example for its lessons. tip(1) and cu(1) functions now might be done by ckermit [L3 ], minicom [L4 ], ...
[Was tip(1) specifically a BSD creation?]