"A fantasy d20-themed dungeon crawler", to quote DarkGod's comment. Inspired by Incursion by Julian Mensch. Made available under Open Game License. This is a non-profit fan project. No money is made. There are currently only two people working on the mod. However, we have released several beta versions so far.
Now that Incursion's open-source and fully OGL, I included Julian's deities - that's 15 deities and 44 domains to choose from. For easier character creation, deity selection comes before alignment selection, so that you can't get yourself into a corner by picking an alignment your desired deity doesn't accept.