FlickBoard is a flicking-style keyboard, in the style of MessagEase and Thumb-Key.
Type the letters in the center of a key by tapping it. Type the keys in the corners by swiping in that direction. That's it!
Release builds are available from GitHub Releases.
You can also build it yourself, by running the following on a computer that is connected to your phone:
$ ./gradlew installDebugThis requires the phone to have USB debugging enabled, and your computer to have the Android SDK installed.
It's proprietary, and is currently threatening everyone's existing installations unless they subscribe.
Thumb-Key intentionally doesn't support some gestures that MessagEase supports.