Complex applications was probably an overstatement but I've created featureful IRC and Discord bots, a database management application and right now I'm creating a graphical browser for the Gemini protocol.
All my other previous attempts at using functional languages, like for instance Haskell, ended up in trivial applications, usually based in numerical analysis.
It's in a very early stage, because I'm porting it from a previous Python code base, so it's not yet available. That said, I'll leave here two links for Racket software that inspire me.
1. Gemini server with tons of features, that I use personally:
All my other previous attempts at using functional languages, like for instance Haskell, ended up in trivial applications, usually based in numerical analysis.