Here a few links to software I wrote: CHICKEN
A mature compiler for the Scheme programming language, targeting C, actively developed and maintained by a bunch of enthusiasts. BONES, another Scheme compiler, targeting x86_64 systems.
?-Prolog, a small and (mostly) complete Prolog-to-C compiler.
Not actively maintained, but may still be useful. ff, a Forth system for UNIX.
GRASS, a Scheme interpreter written in (mostly) R5RS Scheme.
Not actively developed, but should be easy to hack and port. MA, a minimalistic variant of the Acme editor, written in Tcl/Tk.
I use this for my daily work.