I'm going to be slightly unorthodox and say that as long as they're no embarking on the same type of venture, having the same name is more-or-less okay. Nobody with domain-specific knowledge is going to be confused by this, and it's barely even worth picking a fight over. If he wants to call it Limbo, I say let him.

See also Newsqueak (also Rob Pike) and the Squeak implementation of smalltalk.

Would suggest "There is already a software project called Limbo, although it's in a quite different domain." In fact there is already also this: https://sourceforge.net/projects/limbopcemulator/ and the Limbo language is almost definitely not in serious use anywhere. (Having bought a copy of Inferno a few years ago and played with it, it didn't feel like a mature platform.)

Apparently there are more projects than proper nouns. This just makes life more interesting.

>Limbo is a programming language for writing distributed systems

Limbo was

I fixed it for you.