Bruno Meilick's Zwirn [$1.99] seems to borrow a lot of the mood and tactile gameplay from Zen Bound [$1.99 / Free], replacing manipulating a 3D object to wrap it in string with actually controlling the string itself to meet the goals of the 25 included levels.
The four tutorial levels walk you through the basic premise behind the game: A length of string comes from one white dot, and must be extended to the other white dot while laying on top of the various black dots that spot the screen on each level. You don't have much control over the string itself aside from pulling it from the end across the screen, which is where the push pins come in.
Later levels come loaded with different amount of push pins which can be moved around by tapping to pick them up, then tapping again to place them. You then pull the string across the screen, bending it around the push pins, and hold it at the second white dot for a few seconds to progress through the game.
It doesn't take long for Zwirn to become quite difficult, but if you get stuck the solutions are available on the Zwirn web site. The developer also put together the following gameplay trailer, which is worth watching because the way the string responds to your touches is neat:
Where Zwirn left me scratching my head was when it comes to the complete lack of music in the game. So much of the atmosphere in Zen Bound came from the fantastic soundtrack which is completely absent in Zwirn. I've somewhat "solved" this problem by playing the Zen Bound soundtrack (which is freely available for download once you purchase Zen Bound) while playing Zwirn. The difference, oddly enough, is night and day.
Regardless, if you like odd puzzle games, Zwirn is worth a look. The gameplay mechanic of stretching the string works well, and the art style is cool-- You just need to bring your own music.
App Store Link: Zwirn, $1.99