Probably useful for research and prototyping, made available under the BSD/GPL/LGPL, or any other DFSG-compatible license.
Nokia adopted Phonon for multimedia use in Qt 4.4 and are developing backends for Gstreamer, Windows and OS X in the KDE SVN repository under the LGPL.
The Matroska development team licenses its libraries under the LGPL, with parsing and playback libraries available under BSD licenses.
Webfmt, is a platform-independent web-based Ajax File Manager for website, released as open source software under the GPL, LGPL, MPL by Fbis source.
Xynth is an embedded windowing system, released under LGPL, developed for systems with low resources, is an alternative for X Window System.