From the release notes:
OpenGrok is a wicked fast source code browser. http://www.opensolaris.org/os/project/opengrok/
OpenGrok is a fast and usable source code search and cross reference engine. It helps you search, cross-reference and navigate your source tree. It can understand various program file formats (c, c++, c#, java, sh, …) and version control histories like (Mercurial, Git, SCCS, RCS, CVS, Subversion, Teamware, ClearCase, Perforce, Monotone and Bazaar.) In other words it lets you grok (profoundly understand) the open source, hence the name OpenGrok. It is written in Java.
Check also Trond’s blog for the rest of the release notes