Ah, there it is. I was wondering when this would happen.

Facebook used to be involved with the Mercurial community, but it was difficult to work with them. They always wanted to do things their way, had their own intentions, and started to demand that the Mercurial project work the way that Facebook wanted. For example, they demanded that we start using Phabricator and started slowly removing sequential revisions from Mercurial in favour of always using node hashes everywhere, arguing that for their gigantic repos, sequential revisions were so big as to be useless.

Eventually the disagreements were too great, and Facebook just stopped publicly talking about Mercurial.

I figured they would emerge a few years later with their fork of it. They love doing this. HipHop VM for PHP, Apache Hive, MyRock; these are examples of Facebook forking off their development in private and then later emerging with some thing they built on top of it.

The Mercurial project is surprisingly still chugging along, and there are still those of us who actually use Mercurial. I doubt I'll switch over to Sapling, because I disagreed with the things that made Facebook fork off in the first place. But if others like Sapling and this manages to put the slightest dent into the git monoculture, I'm happy for the change and innovation. I really hope that git is not the final word in version control. I want to see more ideas be spread and that people can see that there can be a world beyond git.

I was going to say that they already had started their own successor to Mercurial called Eden, but it seems like Sapling is just a renaming of Eden. Maybe anyway. It's a bit unclear.