I've also experimented with the XIAO processor from Seeed Studio. It's about the size of your thumbnail and costs $5:
It has 256K of flash and 32K of SRAM with 19 general I/O pins, ADC/DAC pins.
I have used earlier versions of this microprocessor and is compatible with the Arduino IDE and libraries...I haven't found a library yet that didn't work, but there may be some. I use this over the Nano--the clock is 2x faster, a lot more memory, and a much smaller footprint. I don't know if it speed is fast enough for T41 I/O duties. More specs at:
jjpurdum