Alternates to Adobe Content Server

i have been experimenting with DRM for books. i have looked around but so far can only see Adobe Content Server 4 as the only credible option.

are there any other - possibly open source - DRM solutions?

option 1: just a DRM solution that can be implemented in a Server.

option 2: a full fledged server with inbuilt DRM support e.g. Adobe Content Server 4.