Marble Mayhem.
Pick a marble. Watch the race. Six marbles, a new course every time, two knockout lines, about forty seconds to a minute.
Fair, and you can check. Each race comes from a random seed drawn in your browser before you pick, and you see its fingerprint first. After the race the seed itself is shown and your browser checks it against the fingerprint, so the race cannot have been changed once you chose. The same seed is the same race on any phone: the link under every result replays it exactly. The starting gate is shuffled every race, and the site's build plays thousands of races to check every colour wins about one time in six.
Free, and nothing to bet. You never stake anything. A correct pick earns coins and XP in Play, kept on this phone; they cannot be bought, sold or cashed out. A replay earns nothing. Race with friends on one screen in Party.