WordPress native revisions for the theme and plugin editors.
This plugin will help you to keep track of changes made to theme and plugin files through the WordPress code editors. You no longer need to worry about possibly breaking something with bad changes because you can always return to an older version of the file. Additionally the plugin helps you to redo your changes when they might have been overwritten by a plugin update by easily showing you what changed. The revisions are handled in a way native to WordPress. Comfortably view revisions using the new revision viewer introduced in WordPress 3.6.
This plugin is part of my Google Summer of Code 2013 project at WordPress. You can find more information on make/core. It was also featured on wptavern.com if you are interested in some background information.