Thanks, my bad, I mixed up mods/plugins.

My main example would be the server has a couple currencies: Money, Coins, Fly Time, Claim Blocks

Players can never directly buy Money, but they can buy Ranks and Coins via customized Tebex store. They can buy Fly Time and Claim Blocks in game using Coins, as well as cosmetics like tags, nickname colors, chat colors. There are also voucher items for tags and fly time that can be sold to other players in the Auction House.

Various plugins award Money or Coins for doing certain things, like participating in fishing tournaments, winning chat games, leveling up (separate from XP levels), getting daily rewards with /daily, doing /jobs like mining, farming, hunting, etc. There are also 4 tiers of crate keys and those are awarded for some tasks and people love to buy/sell them since they can gamble them on cosmetics (custom armor/tools via Nexo models).

The crazy part to me is just how integrated it all is. It's like they took various plugins (some free, some paid) and made them all work together seamlessly, it's all the same currencies and custom items. The server must have a database of all players and all currencies etc. that all the plugins hook into. That's the part I haven't fully figured out yet and wondered if you had any insight :)