Yes, what I meant is that I use a Mac. I'm not sure what you mean by your first sentence; are you saying that I could use a Mac-specific programming language?
I had heard of Mono, but I wasn't sure how practical it was, so thanks for the input. From what you've said, using C# with Mono sounds like a good choice then.
EDIT: My line of reasoning for wanting to make it cross-platform was that most people seem to make their tools Windows-only, so if I need to support another platform, it's probably better to support Windows as well.