Yes, with the new Steamplay Feature, it is possible. It even made it possible to Play against people on the PS3.(look at portal 2) all games Labeled with:
SteamPlay(tm) PC+MAC
are playable on the Mac and can you can play against PC's
No, because you are not using Steam to play the game, you are only using Steam to verify the game and to use the multiplayer parts of it. If you have a Mac version DVD/CD of the same game then you could still use it on steam if you register it on Steam.I THINK if you bought the Windows game on steam they will let you download the Mac version on the same machine. They have the full instructions on their web site.
Yes.On steam it is free for PC and MAC.
Yes, it's possible to play multiplayer games between a Mac and PC. It depends on what game and how you decide to do it.
No. Steam games run on PC/mac and not on Sony PS4 (or nintendo or xbox) at all.
If you want to play the game on a PC or a Mac, yes.
Steam. Its a program that allows you to download PC games. If your on xbox or ps3 you have to buy it in store or in the PSN or XBL stores.
Yes Star Wars Battlefront is Multiplayer for the PC.
As of July 2014, it does not exist for the PC as a multiplayer mode.
Yes. In online multiplayer it is. You can play only multiplayer on Steam. If you want to add me as friend on steam my Steam name is jucks88.
If the game is available On Steam (See links below) you can add the CD Key/serial number by selecting the Activate Product On Steam from the Steam Games menu. Otherwise you can try the Add Non-Steam game option which may or may not find the game in the Mac's drive.
Yes, Multiplayer comes with Minecraft on the PC.
It's likely something at your end depending on your connection or maybe steam's servers are quite busy.