- Early access. Back in the day the dev would pay you with a free copy of the game for helping with the beta. Now you pay the dev for the privilege of helping with the beta.
- Cosmetics. Tons of games have stuff you can buy (equipment, skins, etc.) to make your character look cool. Extra stuff that can be developed easily by an artist, doesn't affect game balance, and sometimes even costs real money.
- Battle pass. I've never bought one but I think you get stuff on two tracks for progression, a free track and a paid track. Progression resets and there are new tracks like 4 times a year or something. Makes people want to open their wallets for the paid track due to FOMO and "...but I already earned it!"
I think if you switch from free to paid you immediately get all the stuff on the paid track you've already progressed past. Also I think they want to charge you $10 four times a year, every time the new tracks come out.
- itch.io -- Sort of like Steam / Epic / GOG for indie developers too small to be on those sites yet.