actually I think that it is basically not used inside facebook anymore. But it is used in a bunch of other companies.
Is that true for ReScript, or no?
Presumably Facebook still uses React? But they use it via regular JS and not Reason or Rescript?
I do have to concur with some of the comments -- the situation seems pretty confusing, and spending a bunch of time looking at docs didn't enlighten me.
It probably explain why fb dedicates so little resources to reason too.