OSS - ###
ALSA (Advanced Linux Sound Architecture) - libasound2
NAS (Network Audio Sound) - libaudio2
esd (Enlightened Sound Daemon) - esound
A sound server that allows multiple sound sources to share a single output device. Presumably the back-end is something straightforward like /dev/dsp, which is provided by the kernel support in the form of either OSS or ALSA.
aRts - ###
libao - libao2
According to the documentation, "Supports ESD, OSS, Solaris, IRIX, and several others"; but the back-end libraries provided by the Debian package are oss, alsa09, nas, esd and arts - essentially the same list as SDL. (What are "Solaris" and "IRIX" in terms of sound support? Presumably operating-system specific back-ends, analogous to OSS and ALSA on their respective platforms.)
SDL (Simple DirectMedia Layer) - libsdl1.2debian
Exists in the following variants: oss, alsa, nas, esd, arts, all - but not libao, which looks like a missed opportunity.
OpenAL - ###

See also the Debian packages alsaplayer-nas, audiooss and timidity, and the JACK Audio Connection Kit (JACK), PulseAudio and ZINF.