Phoronix: Prequengine: Another Open-Source Game Engine
Lately there's been an increasing number of open-source projects sprouting up to design open-source game engine implementations around older closed-source engines to handle certain game content. Another one of these projects is Prequengine, which is for Little Big Adventure...
Well since we're bringing up open source engines, I'll promote CorsixTH for the 1998 Bullfrog game Theme Hospital: http://code.google.com/p/corsix-th/
The community around that engine is currently quite active. Most of the major features of the game have been implemented, along with some extras such as a map editor and community levels.