gs2 is a a concatenative language designed by User:nooodl, inspired by GolfScript and J, designed to be as efficient as possible at code golf. gs2 code uses a binary format in which most bytes represent a single high-level stack operation. The code is run over stdin token by token, just like GolfScript.
The documentation that used to be here is mostly out of date now, and until the author gets around to writing up something more thorough, careful reading of the source code is your best bet, as with FlogScript. An old revision can be found here: