Just like in osu!, you get a shiny yellow username in the in-game chat to show everyone you're a really cool dude who has helped us pay the server bills.
Again, just like in osu!, you will get a donator badge on your profile, to show everyone you're supporting Horizon.
Competing with friends is really cool, you can play on the leaderboard with someone more or less on your level, without getting crippling depression and RSI for not beating that pro!
You'll get exclusive access to the "#donators" text and voice channels, you'll be able to change your discord nickname and you'll get a custom role with custom username colour!
Want to start over one more time? With donator you can! Normally you can only request an account wipe once, but having donated you'll be able to do it once again.
Who knows what we could implement next? You could be able to do even more stuff for donors once we implement it.