Learn the history of early 1990s and 2000s PC gaming!
If you would like to play some of the games mentioned you can go to the following places to download shareware or purchase the games themselves.
Doom IWAD shareware -> doomworld.com
GZ/Z Doom IWAD Loader -> zdoom.org
Steam store Doom and Doom2 -> store.steampowered.com
Steam store Half-Life -> store.steampowered.com
Steam store Half-Life2 -> store.steampowered.com