A Facepunch user by the name "DevinWatson" was recently digging through the now open Steamworks SDK when he discovered references to a possible Left 4 Dead 3 game title hidden in the Steam database. While we already knew that Valve's next-gen engine, Source 2, has been in development for a while, this is the first reference we've seen to a possible third Left 4 Dead title. Before you start complaining about Valve focusing on the wrong series, the SteamDB page notes that this app hasn't been updated in months and shows no signs of active development. Valve are known to experiment a lot and it wouldn't be unusual for them to create and drop a project without any ever announcing anything, though it is worth noting that the user was banned for trying to access the app. However, it has been suggested that the user was actually banned for making too many requests to the Steamworks website when he was running through AppIDs. The user also posts some information regarding Source 2, apparently from an unnamed former Valve employee's LinkedIn profile. The employee was involved in porting Left 4 Dead 2 to the Source 2 engine as a more "real" test case for the engine. Left 4 Dead 2 seems to be a popular testbed for Valve as it has also been used to test the Source for Linux. We don't really know if any of this means anything substantial, but we'll keep you posted if any real evidence of development of Left 4 Dead 3 arises. If you'd like to read more, feel free to check out the relevant thread over on NeoGAF. We'll keep you posted should we learn more.