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.
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.