AstexViewer has just gone open source (LGPL), and is available from http://openastexviewer.net/.
Both Jmol and AstexViewer are 3D chemical structure applets that run in the browser. AstexViewer was originally developed by Mike Hartshorn at Astex Therapeutics for in-house visualisation of protein crystal structures. Although available at no cost for some time, it has not until now been open source.
Jmol is in many ways an open source success story. It has several enthusiastic developers (who make new releases with new features every few days!), a very busy mailing list, a large number of users worldwide, and even a recent book. It will be interesting to see whether OpenAstexViewer is sufficiently different to attract users away from this well-established project.
In any case, here's to diversity. Hopefully both projects will get interesting ideas from each other.