The project page: https://github.com/archagon/tasty-imitation-keyboard
Here's how it got started. I speak Russian, but I'm terrible at typing on anything but the standard QWERTY keyboard, and so I was interested in getting transliteration (along the lines of http://www.translit.ru) working on iOS8. On a Mac, this was as easy as building an "input method", which sits between your input and output and converts things as you type. But on iOS8, if you're building a custom keyboard, you really have to start from scratch. My goal was to make a keyboard that looks pretty much the same as the system keyboard but allows you to change the way it behaves, thus fulfilling the same goal as an input method in a roundabout way.
The behavior isn't perfect. The graphics deviate, there are a few rough performance edges, and there are some features missing (including iPad support). But it works! I made my translit keyboard[1] and got it into the App Store.
[1]: http://translit-keyboard.archagon.net