OK, let's see if I remember well:

OSS is obsolete.

ALSA is a basic primitive way to do play audio streams integrated into the kernel.

PA is an abstraction on top of ALSA that helps with network stuff, per-application volume control, …

JACK is an alternative to ALSA/PA for low latency professional use cases: you can plumb it yourself, connect inputs/outputs, …

PW is an efficient implementation of both PA and JACK, which is better than the original PA in latency.