To that end, voxilla.org tracks, archives, documents, and develops such software. The development focus in on server-side solutions. The definition used on voxilla covers the transception and switching of multimedia streams. There is a brief discussion of these here.
Device drivers provide a software interface to hardware.
Protocol stacks enable programs to speak to each other via commodity protocols. Conversion software is required to convert data between formats. Finally, applications carry out high-level tasks. These four categories have been further broken down and analyzed, and are listed on the projects page. The primary caveat for hosting relevant software here is an open-source license.