There's open-source development work on re-implementations of BioWare's 3D game engines, principally at this point for the Aurora engine as used by Neverwinter Nights.
The developer behind this work has succeeded with a working engine framework, a global configuration sub-system, resource manager, XMV demuxer, basic manager classes of 3D graphics and sound, and much more. Still missing though is the animation subsystem, 3D positional audio, and WMV p-frames.
Specifically for the Neverwinter Nights game this open-source portable version has partially working menus, loading of modules and areas, move support, door interactions, and script execution. However, this open-source community incarnation still lacks area lighting, most script functions, script triggers, walking, combat, and other key features to the game.
There's also work -- with lesser degrees of progress - on Knights of the Old Republic I and II, Jack Empire, Neverwinter Nights 2, The Witcher, Dragon Age: Origins, Sonic Chronicles: The Dark Brotherhood, and Dragon Age 2.
More details on this open-source work can be found in this blog post