Free to play, free of paywalls. Donations keep it that way.
Hosting, the domain, and the email service that sends verification codes and pick reminders. That is the whole list. KOVotes is run by one person as a side project, so contributions cover running costs rather than anybody's time.
Nothing about the game. Donating earns no points, no badge, no rank, and no advantage of any kind, and it has no bearing on prize eligibility. Every feature on the site is free to every account, and there is no paid tier and no plan for one. If that ever changes it will be said plainly here first.
Telling one other fight fan about the site is worth more than a donation, honestly. Reporting a wrong result is worth more again — see the contact page. The leaderboard only gets interesting when more people are calling the fights.