Day of Defeat 2
Day of Defeat is such an underrated game, Valve should remake DOD:S in Source 2 with new features and content like they did with CSGO. Even if Valve couldn't do it themselves they could allow a team of modders to do it themselves, like the TF2S2 project by Amper Software, as long as they require you to have DOD:S, then I'm sure it could be legal. I'm not an expert in copyright laws however.
(Update Dec 4 2024)
If they don't make a new DOD game or a port, I hope they at least make a 20 year anniversary update for it next year. They could add a new faction, add more maps, QOL updates like workshop support and other things to bring the game up to date.
If Gabey sees this, please bless us with DOD 2 or a good update for DOD:S's anniversary