I had come accross this one a while back, was still in beta... forgotten about it since, nice catch ! Maybe I had discarded it because it uses the PEAR librairies, don’t remember...
From the video, I would add metadata schema seems really enterprise class, with Dublin Core properties... also revisionning with rollback... Last but not least, frontend editing seems really good. On top of the video, the overview doc (PDF) contains a lot more info (see this page :
http://matrix.squiz.net/download/documentation)
Definitely worth doing more research on this... I’ll install, check how it behaves (plus the video is from an old version 3.1 while the current is 3.8...). Also, I’ll browse their website and community, see how they communicate and all
Edit : Currently, MySource Matrix only support PostGreSQL and Oracle, not MySQL... their positionning seems to be definitely more the ECM segment...