The PIC32MZ EF series are powerful microcontrollers with plenty of resources, and come in a convenient 64-pin package (other packages are also offered). It is very suitable for the realisation of a Rittle system.
Disclaimer: Rittle is in continuous development. There could be incomplete or missing functionality in the current version, or still unresolved bugs. The author will appreciate highly any feedback or suggestions for solving existing problems or adding more functionality.