I couldn't be more fascinated with alphas, tech demos and canceled versions of games, and the recent unearthing of a tech demo of an early version of the first Half-Life is one of the most fascinating things I've seen in a while. The Alpha, dubbed version 0.52 is a tech demo version of the game which was released on 9/4/1997, a full year before the release of the actual game.
The alpha was leaked via a Redditor called jackaljayzer, who claimed that the early version of the game was released on a disk intended for press purposes only. The preview disc featured a preview of various areas showcasing the type of graphical feats that the heavily modified Quake engine dubbed 'Goldsource' could accomplish, as well as an early version of multiplayer modes.
We're talking pre-Source here, during a time in which geometric transparency, tactical AI and heavily scripted sequences in first person shooters were close to nonexistent, aspects which made the game nothing short of revolutionary at the time. I still get a warm, fuzzy feeling when I remember playing the game for the first time.