Re:Buck – A build system developed and used by Facebook
by sdwilsh on Tuesday March 14, 2017 @11:56AM
(#13868591)
What Facebook uses internally in their monorepo and what they publish to open source for external consumption doesn't have to be the same build tool.
Facebook uses fbshipit (https://github.com/facebook/fbshipit/) to take slices of their monorepo and publish them to GitHub.
Looking at https://github.com/facebook you seem to be using all sorts of build tools...