[muxator]

A good number of engineers from facebbok and google are active developing on mercurial, even if it gets comparatively less attention from the big public.

Facebook also maintains a set of custom extension for it [0], and there is an interesting talk about the reasons beyond their choice [1].

[0] https://phab.mercurial-scm.org/diffusion/FBHGX/

[1] https://m.youtube.com/watch?v=gOVD-DrUpwQ

[lclarkmichalek]

There is also Mononoke, a HG server being built in Rust: https://github.com/facebookexperimental/mononoke

(work for FB)

[muxator]

That's really interesting. I've updated wikipedia mentioning this.