I was looking around on the Steam website and I saw Steam Play
What is that? I don’t understand it and I’m too lazy to figure it out so I’ll just ask you guys 
It means you can play a game both on PC and the Mac
What if you bought The Orange Box for PC before Steam Games for Mac came out? Would that mean you could install the Orange Box for PC on a Mac? Cuz I heard some guy say you could
You own the game on an account. It doesn’t matter on which computer you install steam and login with your account, because the game is linked to your account.
So yes, if you bought OB for pc, before Mac update, you can play it on both platforms.
Also: steam support article
Also: 
hard to notice windows + mac logo?
If you buy a Steamplay compatible game on either platform, you will be able to play on either platform without having to buy it again.
So if you bought HL2 on Mac on your account, it will be automatically be available on your Windows Steam and vice-versa.
If you already own a Steamplay game that existed before that was implemented, you still can get it for Mac.
yay :3
Basically if a game is on both platforms, it automatically supports Steamplay.
Sorry for resurrecting the thread but what if you bought a physical copy of the orange box tying it to your steam account with the key. Would you be able to install it to the Mac using the dvd or would you have to downloaded from steam servers.
Probably need to download it from steam. The orange box was released before that update. There may be some content on the discs that you could copy, like the .gcf files, but I think the disc format might not even be supported. Either way, you’ll have to download the updates & steam over the internet. You also need to sign in to play.
I’m pretty sure you can copy the contents of the folder “Steam/steamapps” on Windows to the same folder on a Mac and you will won’t need to download anything, as long as it is updated.
Not quite. It needs the OSX binaries, but the majority of it is just content, which will work fine.
That is true, though I wonder if it can easily tell that. It could see “Wait, this isn’t the OSX GCF with the OSX binaries. Guess I better trash it and download the whole thing.”
It can tell, I’ve done it. It won’t delete it.