Balloons stream down a fixed path, line it with towers, upgrade them, and pop every wave before a single balloon slips past the exit.
Waves of balloons follow a set path across the map. Build towers on the ground beside the route to pop them on the way through, and upgrade your best placements as the waves get tougher. Stronger balloons release weaker ones when popped, so layers add up fast. Let too many reach the exit and you lose.
Pop Path draws on Bloons TD, released by Ninja Kiwi in 2007, which took tower defence and made the targets layered rather than simply tougher.
A balloon is not a health bar: pop the green one and a blue one is inside it, then a red. So damage does not remove a threat, it converts it into a lesser threat further along your track. Towers that pop several layers at once are worth more than towers that do more damage, and a defence that looks adequate collapses the moment a layer it cannot strip arrives in bulk.
Pop Path is an original free browser game in the path-following tower defense tradition, with free tower repositioning and layered balloon waves. Just open and play.