Half-Life 2: Badlands picks up right after Barney Calhoun's dramatic departure at the end of Episode One. As an unnamed resistance member, you find yourself on a perilous journey out of the city, only to be caught in an intense ambush by the Combine Remnants. Forced to seek refuge in a deserted metro, you and the remaining survivors are now trapped underground as dangerous dark-energy radiation floods the city with no clear escape route in sight.
Nightfall is an HL2RP server for Garry's Mod that is a prequel of sorts to Radiateds story. Sure, you won't have to play it to understand the mod but they do tie into each other.
A passion project of mine I've been working on so that I won't get burnt out whilst writing for and managing Radiated.
Teaser Trailer by Northh