What older games do people still play online that are available here?

Examples I can think of
Doom (a few ways to play online)
M&B Warband (Most evenings has people on in the US, EU is more populated)
Morrowind (TESMP (look it up))
Star Wars Battlefront 2

Any other gems still viable online?
Or anything related you feel like sharing.
Thank you!

(I will clarify, because people will call a game dead if it doesn't have full servers any time of day -- Populated in this case could mean a few servers lightly occupied with people all around the world playing, or ones that just have seldom events)

Re-Volt, which recently was added back to GOG has a source port called RVGL with a healthy online community.

Myst Uru is technically the skeleton from which Myst Online/Live was built.

Quake and Unreal both have dedicated and ancient communities.

OpenTTD has a healthy multiplayer community.

OpenRCT2, which is a source port of Roller Coaster Tycoon 2 is multiplayer capable.

SMAC & Civ IV may not have servers. This shouldn't stop you from playing games with others, as they both have a PBEM option.

Stardew Valley has a functional multiplayer system, but it's less functional on GOG.