Berkelium
Over the past three months, we’ve been working on a new BSD-licensed browser engine called Berkelium. Berkelium is a library that provides off-screen browser rendering via Google’s open source Chromium and takes advantage of Chromium’s multi-process rendering engine, allowing us to safely isolate browser instances.  Best of all, it is independent of Sirikata—you can incorporate it into any project to get a simple, easy to use API for off-screen web browsers.  We’ve started using it in Sirikata to allow arbitrary 3d objects to contain browsers, and in the future, objects may be able to run a user interfaces and even entire object scripts within the sandbox of a browser window.
Berkelium should support plugins, but currently that support is limited to Flash (on all platforms). Hopefully many needs will be addressed by new features in HTML5. For those that aren’t, we believe Flash is able to fill the gap. (For the curious with some spare time, it may be possible to use a hooked HDC on Windows, and to use the X11 Composite extension to render plugins to OpenGL on Linux. However, we suspect enabling arbitrary plugins and programs in this way would take a good month of work to get right.)
And, of course, we wouldn’t leave you without a demo of the browser in action in Sirikata: