Blades of Avernum
Blades of Avernum is an isometric, party- and turn-based RPG created by Spiderweb Software, makers of many other fine RPGs. The game is part of the Avernum series, but it was produced with the explicit purpose of facilitating user-created content. I was one of those users, creating custom adventures in the game's canon.
I spent a good six years working with Blades of Avernum, and that hard work yielded seven finished scenarios, listed and linked below.