Apple opened the door for third-party keyboards on iOS devices with the release of iOS 8.0. iPod touch, iPhone and iPad owners can now download third-party keyboards as applications from the Apple App Store. Once installed users must enable the third-party keyboard on their device in the Settings app. Here's how:
1. Navigate to Settings > General > Keyboard > Keyboards
2. Tap the "Add New Keyboard..." tab
3. Select the newly downloaded third-party keyboard
4. Tap the "Allow Full Access" slider
Once the keyboard is enabled you can tap the world icon on the stock iOS keyboard to switch keyboards.