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.