fallopen - Opensource engine for Fallout 2 RPG written with C#
DarfFO - Fallout 2 game engine written in JavaScript. No source code.
fallout-2-for-linux-source - project originally started by Timeslip. Its goal was to move all sfall hacks to portable C code.
ianout - a next generation 2d engine
sfall - a set of engine modifications for the classic game Fallout 2 by Interplay.
Fallout Wiki - a lot of information about gameplay, file formats, game items, etc.
TeamX - web arhive that contains a lot of vital information about Fallout engine.