Open source remakes spring up all the time, aiming to resurrect older games to run on modern systems that they weren't originally designed to run on, and to provide the bells and whistles that current players expect. For example, Corsix-TH allows Theme Hospital to be played in high resolution on Windows, Mac and Linux. Some engines have made entire generations of games playable on modern systems, for example, ScummVM allows one to play the majority of the LucasArts' adventure games on virtually any system.
What are your favourite open source engine remakes? What worked and what didn't? What new engines in development should we be keeping an eye on?
Here's a handy list of open source engine remakes from osgameclones.com.