I'm not talking about a game you play a few times a month, but a game you're actively playing as one of your currnet "main" games. I'm sure there are retro gamers out there playing some old school games, but curious to see what modern gamers are playing too! :)
For me, probably Overwatch (2016). I recently got back into it the past few months and it's still really fun and still has a healthy population.
I would say Team Fortress 2. I haven't played literally anything in the past 3-4 weeks, but it was the last game I played, and I used to play it regularly. Will probably start playing it again once Scream Fortress (Halloween event) begins on early October.