I have an application that isn't compiled with ALSA support. It is quite old. It does not make me happy but whatevs, it works. I need OSS emulation. Really a simple /dev/dsp device would be fine. Here's how I got it.
apt-get install alsa-oss oss-compat
modprobe snd-pcm-oss
modprobe snd-seq-oss
echo "snd-pcm-oss\nsnd-seq-oss" >> /etc/modules
lsmod
If this all works out and you see the modules you just loaded in the output, you can reboot and check if they load automatically.
That's it!