Probably not still in use, but back in the mid-80's my department bought a fancy computer for use in product testing. I was the young guy, fresh out of school with *some* experience in computers (FORTRAN, BASIC, and a tiny bit of 8085 assembly), so I was expected to figure it out, which I never did.
The thing ran FORTH, which was a niche language. We ended up using it in a project we contracted out to a small company. One of the brainiacs ended up "re-writing the O/S" as it was told to me.