In addition to alien truth there are probably also alien games: ones so simple for their level of depth and enjoyment that you would expect them to be independently discovered. For example, Hex [1] is reasonably deep and has been invented at least twice. Go, with something like the Tromp-Taylor rules [2] might be as well? Probably not Chess, though!

[1] https://en.wikipedia.org/wiki/Hex_(board_game)

[2] https://senseis.xmp.net/?TrompTaylorRules