Meta's Sapling source-code management system

The client is capable of cloning Git repos - that's the example that they show in the blog post. I think the blog post is a little confusing because they've rolled up a whole bunch of good ideas into a single system (which is understandable: that's the system they were using internally). My reading of the blog post is that you can see some of the good ideas, like the way the CLI shows history and handles stacked changes, with Sapling pointed at a Git repo, but other good ideas, like whatever they've done to address large monorepos, require pointing it at a Sapling server.

The blog post says "You can now try its various features using Sapling’s built-in Git support to clone any of your existing repositories." and "Many of our scale features require using a Sapling-specific server and are therefore unavailable in our initial client release."

Note that in addition to the Sapling CLI, they're also releasing ReviewStack, an alternative user interface for reviewing GitHub pull requests. The code appears to be in the Sapling repo, and there's also a public instance of it at https://reviewstack.dev .