Last week at work I used #pikchr for the first time. It's a diagram generator that uses a text file as a source. This means that you can now easily keep track of your diagrams in a VCS (git, bah). It took me a couple of days to get used to the way it wors.
Unluckily right now the site seems down to me, but here's the link:
They have an online version, which is the one I used, but there's also a CLI you can install locally... at least on #Linux.