RabbitVCS is described as 'set of graphical tools written to provide simple and straightforward access to the version control systems you use' and is a Version Control System in the Development category. There are five alternatives to RabbitVCS for Windows, Linux and Mac. The best alternative is TortoiseGit, which is both free and Open Source. Other great apps like RabbitVCS are TortoiseSVN (Free, Open Source), Slik SVN (Free), kdeSVN (Free, Open Source) and gitti (Free).
TortoiseGit is a Windows Shell Interface to Git and based on TortoiseSVN. It's open source and can fully be build with freely available software. Since it's not an integration for a specific IDE like...
TortoiseSVN is a really easy to use Revision control / version control / source control software for Windows. Since its not an integration for a specific IDE you can use it with whatever development tools you like.
kdesvn is a Subversion client using the native Subversion development API instead of just parsing the output of the commandline tool like most other clients do. It tries to setup a look and feel like the standard filemanager of KDE and is integrated into it via KPart.
Gitti is a Git Client for Mac OS X designed to help users never have to touch the command line. With a highly modular and organized interface, Gitti logically separates each step in your Git workflow to maximize your efficiency.