Torchlight - Preview video @ Ten Ton Hammer
Torchlight is a single player action RPG that will be transformed after the release in the fall into an MMORPG (although that will take a few years) also named Torchlight. Torchlight will be released with a modding set that allows the modder to change a lot of the game.
Ten Ton Hammer had an interview with Travis Baldree from Runic Games, the company that was formed by Travis (creator of Fate), Max Schaefer and Erich Schaefer (co-founders of Blizzard North), and the Flagship Studios Seattle team responsible for Mythos. The interview is recorded and you can check it out together with some ingame content and the modding tools right here.