What are some alternatives?
When comparing Bloons TD and Fieldrunners, you can also consider the following products
Kingdom Rush - Epic game of tower defense available across multiple platforms.
TowerMadness - Tower Madness is an epic 3D tower defense game for iOS.
Towers of Oz - Towers of Oz for iPad, iPhone, Android, Mac & PC! Battle wooden soldiers, saber-toothed tigers and giant frogs in tactical battles as you defend the Land of Oz from the Dwarf King!!
Bejeweled Blitz - Our games are sprinkled with a whirlwind of smile-inducing awesomeness and polished to a shiny sheen that keeps the world coming back again and again.
Tower Duel - Tower Duel is a Multiplayer Tower Defense Game for iOS and Android.
Robo Defense - Robo Defense is the ultimate portable tower defense experience.