The name looks like the ASCII face of a confused person o_O. The game, however, is straightforward. A dot is traveling along a circle that is one of a string of adjoined circles. The goal is to get that dot to the other end of the string of circles. The only action the player can take is to move the dot back and forth between the insides and outsides of the circles as it travels.

There are obstacles, of course, which destroy the dot and send the player back to the most recent check point. As fast as the dot moves, though, it's easy enough to flip the dot to the outside of a circle too early, crashing into the point where two circles adjoin instead of making it safely to the inside of the next circle. Fortunately, check points are frequent and the player is never stuck replaying long stretches of a level. Once a level is complete, the best (meaning fewest) number of deaths on a run-through is displayed on the level selection menu.

Every level has a counterpart which is identical except that the visuals waver as if seen through heat waves coming off of pavement. It adds a bit of extra challenge, though I tend to get better scores the first time through on a wavy version than on the original.

oO's levels each have their own associated color, but it shows in the dark background and the inside of the checkpoint circles, which means the colors have no impact on gameplay. They're a purely aesthetic addition which has no effect on playability and mesh well with the simplicity of the gameplay. The background music complements all of this well, too, to create a great experience.

Rainbow Train's oO is only available for mobile devices for $1.99 on Google Play and on iOS.

[The oO Game]