The Readium Projects primary goal is to provide rock-solid, performant building blocks and applications for EPUB3 publications. There are currently three separate projects underway: ReadiumJS, Readium SDK and LCP (Lightweight Content Protection).
There are two parts to ReadiumJS:
In addition, all of the source code for both the Chrome Extension and the CloudReader can be downloaded from github as source code and modified to suit. All of the ReadiumJS sub-projects are available under the BSD open source license
Note that the Readium SDK Core C++ library is dual-licensed: publicly via Gnu Affero General Public License Version 3 (a license which contains terms incompatible with use in closed-source software including a copyleft provision), and via a an Alternative License based on the Apache License which provides additional rights targeted to commercial adopters utilizing Readium SDK in closed-source software, including not having any copyleft provision. For more information on Readium SDK licensing see: http://readium.org/license-readium-sdk
Several members of Readium Foundation are pursuing, as a sub-project of Readium SDK, an implementation of a DRM technology. Readium LCP (for "Lightweight Content Protection") is expected to provide a module for Readium SDK as well as server-side components. Readium SDK will not require use of Readium LCP, which will be separately licensed to interested parties.
More information on Readium LCP coming soon.