It has been an iOS exclusive since it was released last year. However, that has changed, because as of Wednesday it's available on Android devices as well!
Best of all, since it's a free to play, you can play it at no charge. And, since it's one of the few games that's done freemium games right, you can actually completely enjoy it without paying anything for in-game items if you want (although Double Fine would certainly appreciate it if you did, since they had to put money into making the game) since the game's in-game premium currency actually is earned through regular game play fairly regularly.
You can grab it for iOS devices through iTunes and for Android devices through Google Play.Source: Android Police
