ESD will mix the simultaneous audio output of multiple running programs, and output the resulting stream to the sound card.
ESD can also manage network-transparentaudio. As such, an application that supports ESD can output audio over the network, to any connected computer that is running an ESD server.
ESD support must be specifically written and added into applications, as ESD does not emulate normal audio hardware APIs. Since ESD has been around for over a decade, earlier than almost any other sound server, a very large number of Unix applications have support for ESD output built-in, or available as add-ons.
ESD was maintained as part of the GNOME project, but as of April 2009, all ESD modules in GNOME have been ported to libcanberra for event sounds or GStreamer/PulseAudio for everything else.