It annoys me greatly that the megacorps have all these fancy devtools that we plebs have no hope of touching. One example being Metas Sapling, which afaik is their way of making git-compatible vcs perform decently well at their scale. Sure it is nominally open-source, but the readme has enough notes like "Not yet supported publicly, OSS is buildable for unsupported experimentation." to dissuade any casual users. And afaik the others have their own things, mostly even less public.
I appreciate that of such companies Microsoft seems the most dedicated to upstreaming what they can directly into git. Most of those heavy performance features are off-by-default, but they are there to `git config` (or `git maintenance` or `git clone`) yourself.
https://github.com/facebook/sapling