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 and mutable state more than subsequent languages.

Interesting implementations:

• ArduinoForth
• amForth
• Ficl
• FlashForth
• Atlast
• RetroForth
• PygmyForth
• gForth
• BigForth
• colorForth
• CamelForth
• DX-Forth
• eForth
• kForth
• HolonForth
• lbForth
• Mecrisp
• Openfirmware
• PFE
• SPF4
• SwapForth
• SwiftForth and SwiftX
• Quest32
• Win32Forth
• 8th
• pForth
• TpForth
• VFX Forth
• zForth
• UF, written in Tal

Two classic texts by Leo Brodie:

• Starting Forth - online edition
• Thinking Forth

Forth implementation written in Literate Programming style:

• jonesforth
• SmithForth

A wiki about Forth:

• http://www.forthfreak.net/

There is a #forth IRC channel on Freenode, or Libera.Chat.