I think the Starseige Tribes community is still active. They have DOZENS of people, dozens!!
Not to hate on those who love old games but yeah, it's a much smaller community.
It's not all bad, smaller communities mean people know each other better. And there is no eSports money hanging over anyone, it's just a community meeting up to have fun once a week.
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The only reason Starseige Tribes is alive today is because of a large amount of hacking effort to port the game up from Windows 2000 to modern Windows. As well as hack the server software to run you own servers.
Other live games truly die. No one will ever play Concord ever again. Tribes loses support, but hackers can fix bugs and forcibly patch to modern systems
If there is a will, there is a way.