Among the companies listed are Facebook and Microsoft.

This list may not be long or exhaustive but it does show a number of companies who are publicly willing to say they use Haskell. It was started in January.

I can personally attest to several companies I have worked with not mentioned in the list which also use Haskell internally. Haskell is not always the bread and butter of the business software. However, it often has an extremely strong presence for developing internal tools, compilers for DSL's, and (micro)services for various tasks.