smjpeg is an implementation of the smjpeg decoding library, which runs on just about any platform. It comes with one sample decoder, smjpeg_decode (console, no UI).
You can check out smjpeg from Subversion via these simple instructions:
svn co svn://svn.icculus.org/smjpeg/trunk/ smjpeg
You can see the web-based Subversion interface here.