[SonOfLilit]

If you like short interpreter implementations, you might like this: http://code.jsoftware.com/wiki/Essays/Incunabulum

[tromp]

or this interpreter of a lazy lambda calculus based language in 25 lines of (obfuscated) C:

http://www.ioccc.org/2012/tromp/tromp.c

http://www.ioccc.org/2012/tromp/hint.html

[agumonkey]

I love how it demonstrates how recursion/loops and shape/dimension based programming can be both thin, fast and generic