I'm looking for a software to plan sessions

I'm a regular at a local BG hub and until now people keep planning sessions via a whatsapp group. This creates a few problems, such as people asking for players for a game, and then random messages pushing their message out of screen, so people don't notice. Basically there's a lot of people who have games who want to play specific games and people who want to play those games, and I want to find a more efficient way to organize this.

Is there any software that does this? Preferrably open source and self-hostable. I thought I'd try asking first before I bite the bullet and write it myself.