Windows Bridge for iOS
In the late '90s, NeXT/Apple actually had a Cocoa runtime for Windows. It was called Yellow Box (but only shipped as part of Enterprise WebObjects, IIRC). It was closed source, of course, and 3rd parties couldn't ship apps using it.<p>In this bizarro world we live in, Microsoft has rebuilt essentially the exact same thing <i>and</i> has released it as MIT-licensed open source.