Remember Uplink? (No, not that Uplink (opens in new tab) .) Valve called its original demo for Half-Life "Uplink" in 1999. It took place during Gordon Freeman's journey through the spooky Lambda Core, but Valve eventually cut the content, later repackaging it as a separate demo. Black Mesa: Uplink (opens in new tab) reproduces Uplink's levels through Black Mesa (opens in new tab) 's art assets and textures.
Tasked with reactivating an antenna to send a distress signal, players must guide Gordon and his magical, mighty crowbar (minds out of the gutter, kids) through the Lambda complex's radioactive bowels. You'll meet Black Mesa denizens we all know and love: scientists, Barney, Vortigaunts, dead scientists, and headcrabs. Because it was a demo, however, Uplink doesn't last long, but it presents a new branch in Black Mesa's storied saga.
Grab Uplink from Mod DB (opens in new tab) . Note: You'll need the also-free Black Mesa (opens in new tab) for it to work.