We used Mercurial at reddit. We switched to it shortly after switching to Python as our main language, figuring it would be easier to use the one written in Python.

We used Mercurial until the day we went open source. We actually preferred it, but we knew at that point that "everyone" used Git, and we would never be seen as serious or get user contributions unless we switched. That was back in 2008. [0]

We actually self hosted a ticketing system[1] and our own git repo, but since the system we used didn't have pull requests, we had to use the old school method of sending us a patch via mailing list using the git-send-email command, the same way the linux kernel did it.

The best part of this is that we had a launch party for open sourcing in San Francisco. The date of the party was chosen a few months in advance, because it takes that long to plan something in physical meat space. This was basically the first time reddit ever had a hard deadline to get something done.

I was primarily responsible for setting up the ticketing system and code repo, and at the same time, we were switching our actual servers to pull from our public code repo for deployment, for true transparency (and I had to set all that up too).

I actually had to do the final setup to make everything public sitting at the bar at the venue with my laptop about five minutes before we opened the doors. At the time, I had about a week of experience with git! And here I was, operating what was expected to be a very popular open repo that anyone could clone from. Good times.

[0] https://web.archive.org/web/20080619043654/http://blog.reddi...

[1] https://web.archive.org/web/20080622134154/http://code.reddi...

Mercurial, 20 years and counting: how are we still alive and kicking? [video]