FMOD Studio consists of 2 parts:
A low-level cross-platform c/c++/c# API, like OpenAl that allows you to work with sounds from code, and a high-level gui that allows sound designers to work with game audio without programming. The gui is totally inaccessible, but the low-level library is exceptionally well-documented. It handles the mundane tasks of decoding file formats, streaming and such, and is easy to integrate. It is being used by numerous mainstream titles.
A note about 3d sound: FMOD 'fakes' 3d sound by using lowpass filters. HRTF support via third-party plugins needs to be purchased separately. For those that don't need HRTF, it looks like an excellent option.
It is free for non-commercial use. You can also use it for free for 1 commercial title per year with a development budget not exceeding US$100,000 (which is any audiogame out there). Subsequent titles released within that year requires a commercial license.
To learn more about its features, visit http://www.fmod.org/products/