One of my favorite features of Google docs is the fact that it's constantly automatically saving versions of my document as I work. This means that even if I forget to save at a certain point before making a critical change there's a good chance that a save point has been created automatically. At the very least, I can return the document to a state prior to the mistaken change and continue working from that point.

Is there a tool with an equivalent feature for a Ruby coder running on Mac OS (or UNIX)?

For example, a tool that will do an automatic Git check-in every couple of minutes to my local repository for the files I'm working on. Maybe I'm paranoid, but this small bit of insurance could put my mind at ease during my day-to-day work.