It sees quite a lot of use in the traditional finance industry in europe from what I've been told but basically all of that is closed source. However probably

It sees quite a lot of use in the traditional finance industry in europe from what I've been told but basically all of that is closed source. However probably the "biggest" open source project with direct commercial use would be the Cardano blockchain (IOG, one of the main developers for Cardano, is one of the top sponsors for the Glasgow Haskell Compiler as well as a major contributor nowadays). The cardano node implementation is linked here: https://github.com/IntersectMBO/cardano-node https://github.com/IntersectMBO/cardano-node However a lot of tooling for the ecosystem is spread between that org, the IOG org, and the CF org, as well as others. https://github.com/IntersectMBO/ https://github.com/IntersectMBO/ https://github.com/input-output-hk/ https://github.com/input-output-hk/ https://github.com/cardano-foundation/ https://github.com/cardano-foundation/ By no means is this the best example but it is a decent example of an extremely large, primarily haskell based project that sees regular use.