Notice what happens at the 5 minute mark. That is when Rails moved to Github last April.
I'm not familiar with how rails has been developed but I'm guessing the explosion is due to there previously only being a small group of people with commit access, as opposed to a sudden rush of people working on it when it hit github, right?
I think it's mostly just that individuals were being properly credited for patches that they submitted, rather than them going through one of the commiters and the source control tool logging the committer as the patch author.
Yeah that is almost certainly 95% of it. Not like Rails was languishing in obscurity before it went to Github. I just thought the visualization was cool.
Is there an explanation anywhere about what the different aspects of the visualization represent? (colors, for instance)
In the top left corner is a little legend for the colors. The bottom right has the date of the commit. I had to watch in HD and fullscreen to even see them.