Tux Paint for iOS (iPhone, iPod Touch, iPad) (Unofficial)
A 3rd party has ported Tux Paint to iOS, and released an 'App' for Apple iPhones, iPod Touches, and iPads. It is available for free in the App Store as "Tux Paint Free". (This version is not officially supported by the Tux Paint developers, though the developer is participating in the project.)
Compatibility note: The current version of Tux Paint requires iOS version 8.0 or later.