The moment you start working with viewer and OpenSim server code – or even configuration files for your servers and regions, the need for source management tools quickly arise.
An application that will handle both Git and Mercurial code repositories is SourceTree from Atlassian.
SourceTree is a front-end to command line based management of Git and Mercurial and helps take the mystery, and sometimes operational errors, out of managing repositories while giving you a much better view of what has and is happening to your code and revisions.
SourceTree is free and available for both Mac and Windows users.