And Miguel started Mono way before Microsoft made C# cross-platform. At that point they were antagonists.
When Mono came along, the internal position at Microsoft was surprisingly positive. There was a dev slide deck that went into Mono in some depth. And a telling slide that said it wasn't a threat because the performance wasn't competitive at the time.
https://en.m.wikipedia.org/wiki/Shared_Source_Common_Languag...
https://en.wikipedia.org/wiki/Shared_Source_Common_Language_...
I have various snapshots of the Rotor 1 and 2 sources around and they have the SSCLI license. There is a file that contains BSD licensed code (pal\rotor_pal.h).
Thank goodness MS got over their allergy to open source licenses, as they seem to prefer MIT nowadays for their releases.
My apologies for misremembering the details and being snarky. Humble pie eaten and enjoyed. :)