While currently zeptoforth works with STM32L476 and STM32F407 DISCOVERY boards, I am currently waiting for an nRF52840-DONGLE board by Nordic Semiconductor so I can not only port zeptoforth to a board that is not an STMicroelectronics product but also so that I will be able to work with low-power wireless communication, which will be exciting. Unfortunately I was notified that my shipping time may  take longer due to the coronavirus outbreak, so we will see how long it takes for it to reach my doorstep.

[UPDATE: The board has arrived! Now porting can commence.]