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?