Daniel Brouwer has posted a set of Open Source Dungeon Crawl game rules.
From his announcement:
I have recently started work on a set of rules for a Dungeon Crawler, similar to HeroQuest and Warhammer Quest.
They are open-source rules, meaning I encourage people to contribute to the project in any way they can.
The Download Section has everything needed to get started. We still need to thoroughly playtest the game, but so far the playtests I have done myself turned out to be fun. The way I set up scenarios means people can easily come up with their own adventures and either play them with friends or publish them!
Hope to see you there!