Demon Hunter is possibly the first mod for the old Hovertank 3D. Although made at the end of 2006 it is quite less rotten and features an apocalyptic sci-fi/fantasy setting.
Standalone which includes new features and doesn't require any additional files anymore. Only requires Dosbox or similar. Among the new features are: tripping overhead map, animated weapon, destroyable walls and other small things. The old game content (maps, sounds, story) also got a slight overhaul.