Valve has released a Mac-compatible version of the original Half-Life
on Steam. While its sequel, Half-Life 2 and other Source engine based games have been available on the platform for some time, the original 1998 release had been limited to Windows until now. The Steam page for the game hasn't been updated to show Mac compatibility yet, but we at MacNN have confirmed that the game will indeed download and run on modern Macs. Half-Life is available as a $10 download from the Steam store.