Ninjahtic is an action/adventure platformer with elements of puzzle-solving and stealth. While it's progression is linear, the open-ended nature of every level requires exploration of an abandoned civilization located atop floating islands.
A third title in the Ninjahtic series, entitled Nil-Ninjahtic: Ronin, has been Greenlit and is now available on Steam!
http://store.steampowered.com/app/454130