I'm aware of PicoC, Cling (nee CINT), and Ch (commercial), but that's only three. What others are there? I'm curious about canonical C interpreters as well as things that aren't quite interpreting C but are somehow related.

Here is another http://compcert.inria.fr

[08/2011] Release of version 1.9 of the Compcert C compiler. Novelties include a reference C interpreter and stronger semantic preservation results.

Oh, another C compiler! I like collecting these - thanks! :)

Question for anyone handing out unofficial legal opinions:

This one is dual-licensed. There are a small kerfuffle of custom licenses that say "no commercial use", but everything is also variously covered by the GPL (v2 or later), LGPL v3, and BSD 3-clause.

Ref: https://github.com/AbsInt/CompCert/blob/master/LICENSE

I'm curious if I could use this in a commercial setting if I perfectly comply with the various GPL and BSD licenses.

If I could, that could be a problem for this group, because the repo readme (at https://github.com/AbsInt/CompCert) explicitly states "this is not free software."

tcc ?

https://bellard.org/tcc/ has:

C script supported : just add '#!/usr/local/bin/tcc -run' at the first line of your C source, and execute it directly from the command line.

Ah, I forgot tcc. Such an amazing system, so sad that development stalled.

FWIW, I think tcc compiles into RAM, then jmp-s to the result. Pretty much just eliminates the creation of an output file.