Thank you for your response!
I already tried programming with Unity3d on my Mac. It comes with the Mono IDE as standard editor for C# programming. It works perfectly fine.
So I guess that I also should be able to edit, compile, and run the Eco sources on my Mac.
I just ask, since I don't know if there are some specialities in the Eco code that prevent it from being edited or compiled on my Mac using Mono.
So if somebody knows it for sure, it would be great to hear about it.