Oh, I found a small screen sized device (3,5") with built-in : « Accelerometer, ambient light and proximity sensors, compass, gyroscope, barometer, thermometer, RFID... » (just as I was suggesting here).
100% free softwares out of the box, if the box comes in one day (as I was advocating here).
« The Neo900 project aims to provide a Fremantle (Maemo™ 5) compatible successor to the N900, with a faster CPU, more RAM and an LTE modem. » https://neo900.org/
The main interest of this project is it's baseband sandboxing design allowing the user to control, for the 1st time, when the baseband works, and what it can reach inside the phone. Continuing those discussions:
And will support Replicant right away among other OSes (as discussed here).
If you consider the N900 case (screen half, keyboard half), the battery and the NeoN mother board as separate modules, it's even a modular phone (at least as the so called Puzzle Phone) [edit more detailed modules distinction]