Glyphs plugin and script for git integration - time traveling fonts!
Clone this repository with git. (You need git installed anyway, so...)
git clone https://github.com/simoncozens/GlyphsGit.git
Double click the plugin or move it into the Glyphs plugin folder. Now reload glyphs.
Now, every time you save your font, you will be prompted to fill in a summary of the changes you made.
To return to a previous state of the font, choose "View revision history" from the File menu, and double-click on a saved version. You'll be instantly taken back to how the font used to look.