I pressed nearly every single key on my keyboard and still couldn't navigate through the menu. It was really strange to find J (or K or L, one of those) to be "cancel" and Space Bar to be "select." But there are no instructions anywhere: not on this page, not in any nonexistent Readme, and most ironically of all, not in the game itself... and the game's been out for literally over two years.
I don't understand game design concepts like this. You can always fit at least 3 players on one keyboard with configurable keys.