Available from https://flathub.org/apps/details/jp.yvt.OpenSpades #OpenSpades is a free and #OpenSource online first-person shooter created by Ben Aksoy, featuring fully destructible terrain and plenty of game modes (including capture the flag) created by the community.
It would be cool if there was a chapo server for OpenSpades hosted by whoever is hosting the Minecraft one. Might even be able to recruit some people through it if you can register with the server list.