Forth

Forth, invented by Chuck Moore, was the first stack-based language. Forth supports a Concatenative style of programming, although it makes use of Parsing words more than subsequent languages.

Interesting implementations:

• RetroForth
• PygmyForth
• gForth
• BigForth

Two classic texts by Leo Brodie:

• Starting Forth
• Thinking Forth

Forth implementation written in Literate Programming style:

• jonesforth

There is a #forth IRC channel on Freenode.