The one I haven't built yet.
As a part of my keyboard research I have been looking into designing a small bluetooth thumb board for my work tablet. The IT department won't let me plug in any USB devices, but are fine with bluetooth.
I also discovered the Kalq keyboard layout, which is interesting. I'm trialing it on my phone and it's not too bad. It wouldn't be too difficult to change the layout on a physical keyboard either. I'm leaning towards the nice!nano as the>
That's just percolating in the back of my head, though. Other things are a higher priority.