Mono was awesome for what it was, and I'm not trying to denigrate those early efforts, but what it was wasn't really enough to say .Net wasn't Windows only. It

Mono was awesome for what it was, and I'm not trying to denigrate those early efforts, but what it was wasn't really enough to say .Net wasn't Windows only. It didn't support WinForms, so no GUI application built for Windows would work on Mono without a major rewrite. Performance was also pretty bad in my experience. We built an optimization engine while I was in grad school for a funding source that mandated Windows, so we wrote the application in C#/.Net. I would develop on Linux at the time, and I built a version of the application that had no GUI so it could run under Mono, but it was easily an order of magnitude slower. It kind of worked for a small slice of .Net programs (e.g., those that didn't rely on WinForms or any other non-implemented part of the stack). That's about all you could say for it for quite some time.