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.
Oh hell yeah, I used to play the shit out of Ace of Spades but I stopped after the buyout. Think it was Jagex that bought em.