Dived into tcl wiki after writing a program with tkinter (tk python bindings), it's amazing to see a community speak about other paradigms. Reading how they approached FP idioms for instance. I felt this way with perl too. These are two old languages that are mostly ignored nowadays (except for the perl6 has shipped) but they have very interesting ways.

If you're interested in Tcl, you might also like to look at TH1:

https://www.fossil-scm.org/xfer/doc/trunk/www/th1.md

It's a tiny Tcl subset, implemented in only a few kloc. It's used by Fossil as a HTML templating engine but it's easily adaptable for other things. It's small enough to be understood and does an excellent job of demonstrating the core principles of how string-processing languages think.

Tiny Tcl implementations are fun in general and perhaps easier to produce than tiny Scheme implementations — as long as you are willing to concede that everything really is a string. :-) (I.e., no caching binary representations; you have to parse from scratch each time.) In a similar vein as TH1 but with a little more functionality there are Picol (https://tcl.wiki/Picol) and LIL (http://runtimeterror.com/tech/lil/).

Disclosure: I maintain an expanded fork of Picol. The original version of it written by antirez was only ~550 LOC but with suchenwi's additions and mine it is now around 3100. There is a link to it on the wiki page. The change that I am most fond of is making it an stb-style (https://github.com/nothings/stb/) header library.