Fleksy is an alternative keyboard for iOS that I first tested when Launch Center Pro, an initial partner, implemented it a few months ago. Within the limitations of iOS, Fleksy provides a different typing experience that can be faster than Apple's default keyboard.
Today, Fleksy has opened up their SDK for any iOS developer to implement in their apps. The public SDK allows apps to feature colorful keyboards (there are themes) and a button in the Copy & Paste menu to quickly switch to the Fleksy keyboard. These system replacements are much more useful on Android because they can be activated anywhere in the OS, and it'll be interesting to see how many iOS apps will add support for Fleksy as a user option.
Check out the Fleksy SDK here.