PulseAudio emulation for ALSA
The program provides an alternative partial implementation of the PulseAudio API. It consists of a loader script and a number of shared libraries with the same names as from original PulseAudio, so applications could dynamically load them and think they are talking to PulseAudio. Internally, no separate sound mixing daemon is used. Instead, apulse relies on ALSA's dmix, dsnoop, and plug plugins to handle multiple sound sources and capture streams running at the same time. dmix plugin muxes multiple playback streams; dsnoop plugin allow multiple applications to capture from a single microphone; and plug plugin transparently converts audio between various sample formats, sample rates and channel numbers. For more than a decade now, ALSA comes with these plugins enabled and configured by default.
apulse wasn't designed to be a drop-in replacement of PulseAudio. It's pointless, since that will be just reimplementation of original PulseAudio, with the same client-daemon architecture, required by the complete feature set. Instead, only parts of the API that are crucial to specific applications are implemented. That's why there is a loader script, named apulse. It updates value of LD_LIBRARY_PATH environment variable to point also to the directory where apulse's libraries are installed, making them available to the application.
Name comes from names of both ALSA and PulseAudio. As aoss was a compatibility layer between OSS programs and ALSA, apulse was designed to be compatibility layer between PulseAudio applications and ALSA.