Source code for our WebGL globe, Cesium (formerly Geoscope), is now on GitHub. To say the least, we are pretty pumped. This is a real open source project; we are not throwing the code out there and abandoning it, nor are we retaining complete control and just releasing source code. We're doing all development and planning out in the open with the community. There's a public roadmap, architecture overview, contributor's guide, and development mailing list.
Most of us are relativity new to github, and so far it is awesome. In particular, the code review tools are the best I've ever used. The ability to comment on commits and on individual lines of code as if we were commenting on a facebook post is useful. Combined with git's ability to quickly create and merge branches, we are really able to embrace peer review. In fact, our code quality has improved just because we know it will be publicly reviewed when merged into master.
As far as the project itself, we already implemented a lot of features, including streaming imagery from Bing, Esri, OpenStreetMap, and WMS; vector data rendering for polygons, polylines, billboards, and labels; various camera modes; a WebGL abstraction layer; etc. Check out the demos on cesium.agi.com. One particularly exciting feature is that Cesium supports 3D, 2D, and columbus view (think 2.5D, see below), and morphing between them with one line of code.
We have a good start, but there is still a lot of core features left. We're starting to look at streaming terrain, COLLADA models, and precision improvements. If you're interested in using or contributing to Cesium, please jump in.