Meld is a visual diff and merge tool. It integrates with most version control systems. The diff viewer lets you edit files in place (diffs update dynamically), and a middle column shows detailed changes and allows merges. The margins show location of changes for easy browsing, and it also features a tabbed interface that allows you to open many diffs at once.
Hgfs is a read-only filesystem interface to Mercurial repositories. The interface gives access to the commit message, manifest, and files of each revision, and to .tgz's of each revision (the .tgz's are generated as they are read). The filesystem is a front-end for the Mercurial library that comes with it. All code is written in Limbo, for Inferno.
TurnKey Revision Control Appliance is an integrated revision control server combining the best open source version control systems: Subversion, Git, Bazaar, and Mercurial. A Web interface is included for each system, making it easy to browse through the code base, compare revisions, and manage repositories for multiple projects. No configuration is required and security patches are automatically installed. A Web management interface, configuration console, and AJAX Web shell are provided. To minimize footprint the appliance is built from the ground up with the minimum required components. It runs everywhere thanks to multiple build formats, including an installable live CD, a VMDK with OVF support, and an Amazon EC2 AMI.
repos-tools is a set of command-line utilities to make work on your code repositories faster and easier. It lets you push, pull, build, and do other things on your repositories all at once. The supported (D)VCSes are Git, Subersion, Bazaar, and Mercurial. For GitHub users, forking, following, watching, and dealing with issues can be done from the shell.
pepper is a commandline tool for retrieving statistics and generating reports from source code repositories. It ships with several graphical and textual reports, and is easily extensible using the Lua scripting language. It includes support for multiple version control systems, including Git and Subversion.
RhodeCode (formerly hg-app) is a Pylons framework based Mercurial repository browser/management with a built-in push/pull server and full text search. It works on http/https, has built-in permission/authentication (+ldap) features. It's similar to github or bitbucket, but it's supposed to run as a standalone hosted application and it focuses more on restricted access to repositories. It's powered by a VCS library that can handle many various version control systems.
AgileSCM is an application lifecycle management solution for Subversion, Git, and Mercurial. It allows you to spend more time developing and less time fighting development tools or tied up with administration. AgileSCM is a user friendly, browser-based interface which abstracts developers from the complications of SVN, Mercurial, and Git.