Something really wonderful is singing together as a community. Just like... for fun! I know a lot of people associate that with Summer Camp but like idk it's super fun and it costs nothing. We do it a lot in Jewish spaces and I also encountered it in Unitarian spaces and I just think it's super lovely.
Another free thing you can do is dancing. As individuals and as social dances like Square, Contra, and Salsa.
Also, for non-social activities, I highly recommend going for walks on a nice sunny day :3