Atomic Monks
Every few levels you could pick a perk. If you'd donated you could get a special Uber perk. The uber perks were powerful but not game-shattering. The game itself was free and none of it was paywalled, but you could effectively buy "cheat codes" this way. The game was PvE so you didn't get the infamous whales problem.
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| Perks; Uber perks were for donors |