[T-R]

Facebook's spam filtering: https://engineering.fb.com/2015/06/26/security/fighting-spam...

[agentultra]

They also occasionally contribute libraries like Haxl [0] and HsThrift [1]

[0] https://hackage.haskell.org/package/haxl

[1] https://engineering.fb.com/2021/02/05/open-source/hsthrift/