DikuMUD
DikuMUD is a historic open MUD family (C codebase, room/mobile/object model, fight and skill loops) that shaped countless fantasy text worlds.
Nilgiri's relationship
Nilgiri is Diku-descended. Older Nilgiri content lived in Diku-style files; Code Law notes that DOM / XML tooling helped convert those files into the Neo-Nilgiri format. The live game is Java (Neo-Nilgiri), not a stock Diku binary.
Player experience still feels Diku-familiar: directional movement, look / exits, shop and rent tropes, city guards, and classless skill trees layered on rolled stats.
What this page is not
This is not a full history of DikuMUD, nor a claim that Nilgiri is unmodified Diku. For Nilgiri-specific systems, prefer Game Law and Code Law.