If I'm not mistaken those guys appeared on the scene back in 2006/2007. They showed off Pixelmator at WWDC and it went down pretty well but that's still their only product, apart from an iOS version.

I guess another way to look at it is this: If you had an idea for a desktop app today, would you decide to write for Mac first using a proprietary language Swift and proprietary SDKs like CoreData or would you pick C# and .NET so the bulk of your code could be re-used on both desktop and mobile, and you could bind to native toolkits for the UI?

Honest question, not snark:

Who are some big C# developers that create major applications consumers (Not enterprises) use everyday?

You mentioned the paucity of major OSX/iOS developers, but I'm not sure the case isn't the same for C#/.NET.

My first thought is any game written in Unity. Works on desktops and android more or less out of the box and iOS with a little bit of tinkering.

Supergiant Games (Bastion and Transistor) and Squad (Kerbal Space Program), to name a couple. And all the StackExchange sites are made on ASP.NET, if you want to count that too.

The Unity-oriented stuff are good examples. The Stack Exchange sites came to my mind as well, though I was hesitant to count web apps.

Neither! I'd say "fuck that nonsense" and go do something else.