Valve announced earlier that they were gonna release Half-Life series of games for Mac (1984 Apple ad Parody). Today is the day… as of the time of this post they aren’t showing in Steam on mac side yet but I was able to trigger the downloads via simple steam:/// urls.
No status on playability but the downloads are trigger-able.
(Behind the scenes of the screenshot)
Here are the links:
Update: Only seems to cover Half-Life 2 series