Star Wars Jedi Knight: Jedi Academy originally launched in 2003 and was based on the Quake III engine. It hasn’t been available on the Mac for a while though, despite the Windows version being available on Steam for some time. As of today though, it’s available from the Mac App Store.
Publisher Aspyr have posted a lengthy FAQ with details of the release, and notes that (although not available until the 31st) the Steam version will be SteamPlay-enabled, meaning you’ll get the Mac version if you’ve already got the Windows version tied to your Steam account. Aspyr also note that there will be “no differences between builds” of the game (although there’s no information on the state of the multiplayer side), so there’ll be no worries about picking up the App Store edition.