Snapkeys just launched Q4 Keyboard. It is a QWERTY keyboard with just 4 keys. Sounds impossible? Watch the video later to understand how to use. BTW, it is free to download at Google Play Store.
Here is the introduction video.
I have tried it for a few minutes. Will need more time to get used to it. I find that some of the features are interesting like able to shift the keyboard around and also save on the footprint of a standard QWERTY keyboard.