What is TclHelp? One occurance is a Tk application interfacing to the TclX help system. However, another is:
The file named e.g. tcl83.hlp that comes with Windows installations of Tcl, a Win-specific-formatted bag of all Tcl/Tk manpages. A shortcut to it is installed in the start menu as "Tcl Help" and beats man on bash quite heavily - even if I'm developing on Sun, I prefer to check that hlp file - decent layout, hyperlinks, etc. Must have been part of Scriptics installations (but Windows only) since 8.0 or so.
Where does one get it? For the Tk app, download, configure, build, and install TclX.
What does it contain? The Tk app appears to 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. Perhaps some Windows user can discuss the tcl winhelp contents?
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.