Zero+ came out in 2015.  I wasn't intrigued enough to try it.  But last week it was listed as Free.
  At first, I didn't think I'd like it, however I was wrong!  The object is to slide your negative numbered tiles onto the positive numbered tiles to they turn into zero.

What's Cool

1. There are blocks (the white X squares) and directional lines and curves.
2. Look at the last image. Look at the most middle white square. The right curve is darker: that is the active curve.  After a tile passes over it, it will toggle to the other curve.
3. Non Equal Tiles. A Negative 4 can go to a Positive 1. It will then become Negative 3 and then can change directions. 4. There is an undo button. Obviously, not a big deal, unless you've been playing games that don't have this.
5. The graphics are very good and most importantly, the puzzles are at a perfect level of difficulty. That is: Hard Enough that I get stuck, but easy enough that I'll solve it after 5 tries.

There are 120 levels and at the moment, I've done 60.

http://thezeroapp.com/
https://itunes.apple.com/us/app/zero+/id944791433"ls=1&mt=8

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