I'm sweetening to this one, it's a free open source collectible card game, with single player and multiplayer capabilities, available for download on windows, mac and linux!!
http://argentumage.com/
https://www.gamingonlinux.com/articles/argentum-age-is-an-open-source-collectible-card-game-with-singleplayer-and-multiplayer.10517
Hello again! I still have several servers that I use for my own projects but don't use anywhere close to their potential so I am offering to share these servers with would-be Argentum Age operators for free. If you don't mind sharing a server with me just let me know and I can get you set up. :) Just go to https://ArgentumAge.GamePlayer.club/HostSplash, choose the "shared" plan and check out using the "offline" payment method so you don't have to pay. Be sure and put that you are wanting the free shared hosting offer in the comment field. You will get a shared Linux server running Argentum Age... If you decide to cancel or switch hosting companies you will get a tar file to install on another host...
If you have any questions just ask!