"Bloons Tower Defense 4" is available for free online play at NinjaKiwi.com and Kongregate.com. "Bloons Tower Defense 4" is also available on Android and iOS.
In "Bloons Tower Defense 4," the player is tasked with defending a track from oncoming balloons. At the beginning of each round, the player positions defensive weapons on the track. The player then clicks Start Round to initiate the next phase, where the balloons advance along the track. The defensive weapons attack the balloons automatically. At the end of the round, the player can use currency acquired from destroying the balloons to purchase additional defensive weapons.