libdvdcss is a sub project of VideoLAN, developed for the VideoLAN client. libdvdcss is also used in other video players such as xine, Mplayer and Totem.

libdvdcss portability means that there are versions running on Linux, Windows, OSX, Solaris and BeOS.

In the US, under the DMCA law (and potential patent laws), it is possibly illegal to distribute libdvdcss thus some distributions such as Ubuntu do not package the library with their official distribution. The question whether libdvdcss is legal or not has never been court tested, so there is no conclusive answer as to whether it can be used and distributed legally.  (http://swik.net/libdvdcss)