Earlier this month I mentioned a nice straightforward guide on using the new iOS 8 custom keyboard extension.
Here’s a project that aims to help solve this issue called Tasty Imitation Keyboard from Alexei Baboulevitch.
Tasty Imitation Keyboard provides a custom keyboard with a similar look and feel to the native iOS keyboard, but can be used as a baseline for creating 3rd party keyboards. The entire keyboard is drawn using Core Graphics, and utilizes auto layout for easy customization.
You can find Tasty Imitation Keyboard on Github here.
A nice starting point for those working on custom keyboards.