Half-Life 2 RTX
Half-Life 2 RTX is the second Nvidia RTX remix to run on Source. It, as the name implies, is a RTX revamp of the original 
Half-Life 2, similar to how Portal was revamped with Portal with RTX. Being developed by Orbifold Studios, it aims to revamp the entire game with RTX lighting, PBR textures, etc. This game was also promoted by 
Nvidia via their official 
YouTube channel.
As of time of writing, only Dr. Kleiner's lab has been revealed in the initial trailer, along with an updated HEV suit. Plus the floor textures now utilizing ray-tracing (or parallax cubemapped[confirm]) reflections.
Via Portal with RTX you can use RTX remix with Half-Life 2 via loading the map files, a tutorial can be found here. However, this method is highly buggy (as is running Half-Life 2 on Portal regularly), and lacks PBR textures.