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 and version control histories like Mercurial, Bazaar, Git, ClearCase, Perforce, SCCS, RCS, CVS, or Subversion. In other words, it lets you grok (profoundly understand) the source.
TkCVS is a cross-platform, Tcl/Tk-based GUI for the CVS and Subversion configuration management systems. It displays the status of the files in the current working directory, and provides buttons and menus to execute CVS, Subversion, or RCS commands on the selected files. The Log Browser displays a branch diagram of the revision history. The Module Browser extends CVS with facilities for a user-friendly listing of modules in the repository. TkDiff is included for browsing and merging your changes.
Chora is built upon the Horde Application Framework and provides a read-only browser interface to any number of version control repositories. Advanced features include a visual branch view of the repository's history, pretty-printed output, annotation, patchsets and basic statistics.