You're always running, the only thing you control is the jump, so time your leaps across a skyline of crumbling rooftops and chase distance.
Your runner sprints automatically across the rooftops. Each building ends in a gap, and roofs give way beneath you, so the single decision is when and how long to jump. Hold the button longer to leap higher and farther. Miss a gap and the run is over, distance is your score.
Rooftop Run draws on Canabalt, released by Adam Saltsman in 2009, which is generally credited with popularizing the endless-runner genre and did it with one button.
You cannot control your speed, only when to jump, and you accelerate continuously whether you like it or not — so the game grows harder without ever changing its rules. Hitting a crate slows you slightly, which makes obstacles a tactical resource rather than pure loss. Everything is in greyscale, the runner flees a threat that is never explained, and the restraint is much of why it works.
Rooftop Run is an original free browser game in the one-button endless-runner tradition, with variable-height jumps and a daily skyline. No install required.