OSS

Open Sound System is the original sound system for Linux and used by many Unix based Operating Systems. Despite having shit USB support, it can produce fantastic sound with tons of options for complete control. Unlike ALSA which is software level, OSS runs at Kernel level providing low latency output and input. Basically, if you're a musician or enjoy high quality sound, you'll want this.

Why ALSA Exists

Back in the day, some jackass contracted 4Front and thought it would be a great move to make OSS4 proprietary. When this caused a stir, Linux developers created an Open Source (Linux only) alternative, ALSA (Advanced Linux Sound Architecture), which despite its name, was never that advanced.

Finally in 2007, 4Front fixed their mistake and made OSS4 completely free and to this day they update it with sources licensed under BSD, CDDL, and GPL.

In Comparison to ALSA

1) Can produce better sound (at least many claim this, and there are options to configure this).

2) More control over your soundcard and other equipment.

3) Fast as fuck (low latency).

4) Kernel based where ALSA is software.

5) Can control volume of each program and don't need to get shitty PulseAudio to do it.

6) Legacy support (older Unix/Linux programs and games), ALSA's OSS emulation sucks balls.

ALSA Advantages

1) Better USB Support.

2) More programs use ALSA.

3) Uh...

Support

While it's no guarantee that OSS4 will work on your system, you can always contact the developers behind it who tend to be kind and helpful. There is also not as much adoption for OSS4 versus ALSA, however:

Anything SDL based will use OSS4 (like Steam and Valve Games)

Anything OpenAL based will work.

Anything GStreamer based will work.

Flash can be configured to use it.

XMMS, Xine, VLC, Mplayer, all work with OSS4.

Wine has an OSS Driver by default (which just got improved recently).

And so on...