The Wintermute Engine Development Kit got a significant refresh over the weekend. Wintermute is an adventure game engine for the creation of 2-D and 2.5-D (3-D characters against 2-D backgrounds) games. The 1.8 update includes support for DX9, Hardware T&L, a WindowEdit tool for dialog boxes, integration with Vista's Game Explorer and many more features.
Wintermute is free for both hobby and commercial projects and is supported solely by donations. A comprehensive list of games using the engine can be found on the Wintermute website.
For a full list of improvements in version 1.8, stop by the official announcement thread.