Open source community rewrite of the Heroes of Might and Magic III engine.
From the VCMI wiki:
The purpose of VCMI project is to rewrite entire HOMM 3: WoG engine from scratch, giving it new and extended possibilities. We hope to support mods and new towns already made by fans but abandoned because of game code limitations.
VCMI is fan-made open-source project in progress. We already allow support for maps of any sizes, higher resolutions and extended engine limits. However, although working, the game is not finished. There are still many features and functionalities to add, both old and brand new.
As yet VCMI is not standalone program, it uses Wake of Gods files and graphics. You need to install WoG before running VCMI.