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.
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.
0release is a program to generate source and binary releases automatically. With minimal configuration, 0release will generate a source tarball release candidate, build it to create a binary archive, upload them to your Web server, check the uploads, and tag the release in GIT and update the version number. It can run unit-tests and custom actions, such as building documentation, etc. For Zero Install users, it can also upload a signed XML metadata file about the release, allowing these users to upgrade automatically. Releases are signed with your GPG key.
gitg targets cases where it is useful to provide a graphical representation of Git data or actions. The history view is a good example, where graphical representation helps to get an overview of the repository. gitg does not aim to be an advanced tool that allows access to every feature of Git through a graphical interface. However, it will try to incorporate common actions that might require multiple actions on the command line (like staging, unstaging, reverting, and committing).