Nat's company Xamarin was acquired by Microsoft in 2016.
HockeyApp wasn't A/B testing, but a platform for iPhone, Mac, Android, and Windows Phone developers to distribute their beta version (like what TestFlight is today to the App Store), collect crash reports (like what Sentry is today), user feedback, and basic analytics for developers.
The Ximian thing I wrote from obviously faulty memory (I now wonder if it was influenced by early 2000s Miguel's bonobo obsession), the rest from various google searches. Should have gone deeper.
https://en.wikipedia.org/wiki/Ximian
Ximian, Inc. (previously called Helix Code and originally named International Gnome Support) was an American company that developed, sold and supported application software for Linux and Unix based on the GNOME platform. It was founded by Miguel de Icaza and Nat Friedman in 1999 and was bought by Novell in 2003
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Novell was in turn acquired by The Attachmate Group on 27 April 2011. In May 2011 The Attachmate Group laid off all its US staff working on Mono, which included De Icaza. He and Friedman then founded Xamarin on 16 May 2011, a new company to continue the development of Mono. On 24 February 2016, Microsoft announced that they had signed an agreement to acquire Xamarin.