Best multiplayer games ideas for office party, group integration, it?

We organize remote office parties from time to time and I thought about playing some multiplayer games with our team. Extra points for someone who suggest something else than chess, boards games or playing cards!

The requirements: - free - easily accesible - no registration if possible - fun!

I have found already: - http://www.quakejs.com/ - https://openarena.live/