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).
gitolite is an access control layer on top of git. It allows you to setup git hosting on a central server, and have multiple "virtual" users (i.e., not "Unix" users) access multiple git repositories, with fine grained access control (read control at the repo level granularity, write control at branch/tag/file/dir level). It has several other features, comprehensive documentation, does not require root permissions, and does not depend on anything except git, Perl 5.8 or later, and any POSIX shell.
owl2vcs is a set of tools designed to facilitate version control of OWL 2 ontologies using version control systems. It contains a commandline diff tool for OWL 2 ontologies integrated with Git and Mercurial. It detects axioms additions and removals, imports' additions and removals, ontology annotations' additions and removals, prefix additions, removals, modifications, and renames, ontology IRI and version IRI changes, and ontology format changes. It supports RDF/XML, OWL/XML, OWL Functional Syntax, Manchester OWL Syntax, and Turtle. It provides a changeset serializer and parser, two formats of changes, compact (like OWL Functional Syntax) and indented (the same, but more readable, using indents instead of parentheses), and four formats of IRIs: Simple, QName, Full, and Label.
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.
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.