Each with their own rules, whether or not ID verification is mandatory or literally illegal, style of voting (mail vs in-person), ballot design/UX, what languages the ballots are in (are ballots in Sweden in anything but Swedish?) and mutually incompatible equipment. There are thousands, if not tens of thousands, of ballot designs in use for the current election.
When viewing this at a macro level for electing the office of the President, it seems absolutely insane.