A college friend named Zach Barth was incredibly into this sort of thing, a game where the rules and units were made up as the game progressed. He tried quite a few times to make such a game, usually called infini-something such as Infinitron[1] and later Infinarena. The [1] link talks a lot about the challenges that came up trying to make such a game and I think its a neat read if you're into this sort of thing.
It's very understandable why these sort of games don't take off very often, as Z. writes in the [1] link on What Went Wrong:
> Unfortunately, the things that made the Infinifranchise great are the same things that made them alienating and, at times, ridiculous. It’s very hard to be creative on demand, which can lead to games that are draining and not terribly spectacular if the players aren’t in the groove. As a result, the games tended to have a limited audience and be overly complicated, although this is most definitely also a consequence of me.
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Zach is also the guy who made Infiniminer[2], the sandbox mining game, and if it looks like a precursor to Minecraft, that's because it was.
I haven't talked to him in a while but Zach these days mostly makes indie engineering puzzle games, you should really check them out[3].
He also made SpaceChem, which is possibly one of the greatest games of all time. I can't recommend it strongly enough. There's a demo on his site and steam. Go try it.
(OK, one caveat - programmers/logic puzzle types may like this game more than the average member of the public.)
It's very understandable why these sort of games don't take off very often, as Z. writes in the [1] link on What Went Wrong:
> Unfortunately, the things that made the Infinifranchise great are the same things that made them alienating and, at times, ridiculous. It’s very hard to be creative on demand, which can lead to games that are draining and not terribly spectacular if the players aren’t in the groove. As a result, the games tended to have a limited audience and be overly complicated, although this is most definitely also a consequence of me.
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Zach is also the guy who made Infiniminer[2], the sandbox mining game, and if it looks like a precursor to Minecraft, that's because it was.
I haven't talked to him in a while but Zach these days mostly makes indie engineering puzzle games, you should really check them out[3].
[1] http://thesiteformerlyknownas.zachtronicsindustries.com/?p=6...
[2] http://thesiteformerlyknownas.zachtronicsindustries.com/?p=7...
[3] http://www.zachtronicsindustries.com/