What is TclHelp? a Tk application interfacing to the TclX help system
Where does one get it? download, configure, build, and install TclX
What does it contain? It appears to me to primarily be just a GUI interface to TclX's help. This help facility is a textification to the man pages for Tcl, plus a structure where an extension COULD, if one so wanted, add their own help information.
For what platforms is it available? Any place that Tk, Tcl, and TclX is available for building.
See also Tkman which is even better, in some ways, in that it hyperlinks any man page in the user's MANPATH.