Interestingly, FreeBSD and Linux both started with the same audio stack (OSS) and both rewrote it twice[1], but FreeBSD has kept the original OSS API while adding essentially the same features, it seems.
The big selling-point of ALSA, from what I remember, was that OSS couldn't provide mixing to support multiple applications - but FreeBSD's OSS does that. Some of the main selling-points of PulseAudio are per-application volume, low latency and high-quality resampling, all of which FreeBSD's OSS claims to do as well.