Ecosystem's the word I'd use in that sense: Macbook, OSX, iTunes, IOS, Facetime. Platform if I was talking about, say, OSX or IOS on appropriate hardware that Facetime runs on.
I might say universe if I was considering a wider issue, like the conventions for terminating lines in text files. OSX is part of the Unix-verse in that sense.
As a *nix jibbler I tend to reserve 'environment' for environment variables, though it would be perfectly reasonable to use it to describe, say, the flavours of computers on a LAN.