Half-Life Alpha

The Half-Life Alpha is a leaked CD comprising materials from Half-Life's 1997 development cycle, before the current rendition was begun.

Details
The game plays on a modified Quake engine, with several unfinished scripts such as the HUD. Due to its glitchy nature, maps can be only accessible by console. (ex."map c1a1") There are 21 maps included. For some reason, only 3 weapons are include, suggesting that most weapons weren't even scripted by this time. The origins of this CD is that it was shipped as a preview for media outlets, not accessible to the general public.