From the home page:
     GSI is an easy to use audio system which can be used over a network
     and which gives applications, through a very simple API, sample
     playing with stereo, 3D, doppler effects, music playing (MIDI, HMP,
     MUS), cd playing and ejecting/changing.

     GSI also contains a separately usable sound/music
     loading/saving/format conversion library libgsif
     (au/aiff/voc/wav/raw, midi/hmp/mus), although saving/format
     conversion is not completely done.

     GSI runs on any unix system that has generic /dev/audio (8000Hz mono
     mulaw), OSS, ultrasound project drivers, or NAS (well, it did once, I
     need to update the NAS stuff), e.g. Linux, OpenBSD and FreeBSD. CD
     playing is dependent on the OS' ioctl's and structs so that probably
     works on linux/*BSD only (Solaris may work, as it seems to use the
     same ioctl's/structs as Linux).

License:  2-clause BSD-style for code / public domain for headers
WWW: http://gsi.sourceforge.net/