SteamDB has reportedly found a treasure trove of games coming to Steam, including Half Life 3. It's been a while since anyone has had an excuse to use a "Half Life 3 confirmed" meme, so now seems as good a time as any.
The leak comes from a minor change Valve made to Steam that revealed a bunch of package info:
Valve recently implemented functionality to automate some frequently asked Steam support questions such as permanently hiding a game from your Steam account and these package names being exposed are a result of them not hiding them when they added this. A similar issue occurred with app names as well.
The full list of games that may or may not be coming soon to Steam includes not only HL3, but Bad Rats Show. Check it out:
Believe if you want to, but it seems unlikely that Valve would be this careless. Third party developers are apparently able to name their packages whatever they want, so someone may have just been making a joke.