Comet.

Comet is a free arcade game that runs in a web browser. There is nothing to download and nothing to install, on a phone or on a computer. You hold one button, or press the screen, and the comet climbs; let go and it falls. That is the whole control.

Every player in the world flies the same course for a week. The course changes every Monday, so the week you join is a week you can win. Every run is replayed on the server from the taps you made, so a score only counts if the game can reproduce it.

The highest score when the week ends wins $100. Entry is free and always will be: the prize is paid for by the advertiser whose brand flies over the city that day, not by players. The winning run is published afterwards, so anyone can replay it and check the result.