This is the main page on for the ReadiumJS project, which is developing a JavaScript library and viewer for EPUB 3 rendering optimized for use to render EPUB files directly from websites and in browser-based "cloud" readers. Using ReadiumJS does not require any server-side infrastructure or browser plug-ins. ReadiumJS shares common JS modules with the Readium SDK project which targets native apps. 

A Readium Chrome Extension is also available and can be installed from the Chrome Web Store. It is one of the most full-featured EPUB 3 Reading Systems available.  The curent version, released September 11, 2014, is 2.15.2.

The Readium project is also developing a cross-browser (as opposed to a Chrome Extension) implementation based on most of the same sources (but with a different viewer/application front end).  This is currently functional but incomplete.

All of the ReadiumJS sub-projects are available under the BSD open source license (Readium SDK components, other than the common JS modules shared with ReadiumJS, are available under a dual license model),