In support of the upcoming Steam for Linux release we have made Half-Life 1 available on Linux and Mac OS X.
This beta involves significant changes for all platforms and your testing is appreciated, please report any bugs to our GitHub page.
Linux and OS X users can simply install the Half-Life application to access the beta. For Windows users right click the game in your Library, choose properties and then go to the Beta tab. Select the SteamPipe beta to start testing. Under windows to opt out of testing simply deselect the beta option on this same page.