https://github.com/diaspora/diaspora/commits/master?author=judytuna
I only ever made two very tiny less-than-one-line commits, and they were both infinitesimal css tweaks, but this was seminal for me because it was my first-ever code contribution to foss. SarahM was delighted (I could only do it because she was so delighted, really -- else I would have been too scared to even look) and accepted my pull requests immediately and said to me on irc, "An open source contributor is you!"

I suppose I also helped with hosting a Diaspora* hack day at Blazing Cloud, and used Cubbi.es.

In early 2012, with ultrasaurus' help, I herded my Women Who Code SF rails study group through several months of designing, coding, and testing an early revamp of Bridge Troll. Since then, several other Railsbridge organizers have taken up the reins, but in those months we learned a lot not only about Rails in the wild, but also how much git spaghetti can be produced even with only 5-20ish active contributors, how to get people involved and invested and come back again, and how much energy it takes to be a heater (in the "to boil the ocean, turn every 10th molecule into a heater" sense of the word).