To elaborate on the above a bit, for me the choice between Jim Tcl and the "big" Tcl 8.x comes down to choosing between vendoring the dependencies and embedding the runtime (Jim Tcl) vs. using the distribution libraries and extending the runtime (Tcl 8).
Either way you get a very fine C library that prevents you from succumbing to Greenspun's tenth rule, so I can only recommend it for most C programs and libraries of sufficient size and complexity.
Oh yes, it is pretty widely available. What I meant was that it was smaller and easier to vendor: for example, you can produce an SQLite-style amalgamation file for it.
Either way you get a very fine C library that prevents you from succumbing to Greenspun's tenth rule, so I can only recommend it for most C programs and libraries of sufficient size and complexity.