Klein Frage

[Chilvence]

I just happened on this game randomly, bought it by way of the humble indie bundle, and I have to say I am impressed. It has that same feeling as when I first played Myst, which is something I haven't had from a game in a very long time. Not much replay value in myst unfortunately....

I want to buy the full series, but I am stuck on a choice I don't want to make. Are the Mac/Windows/Linux versions supposed to be different purchases, or can I not just buy it once and run it on whichever operating system I feel like? I love the fact that it's cross platform, but because I happen to be running windows at the moment, I dont want to have to give up the option of running the game linux later... (well, if half of my favourite games ran on linux, then windows would be in the bin already...)