I have an ESP32 set up with Zimodem which just makes the ESP32 act like a Hayes modem that talks IP instead of phone numbers to the serial port. They're a ton of fun.
FujiNet appears to offer a little bit more in the way of high level service translation.
On the off chance someone hadn't heard of it - Fujinet is amazing! ( fujinet.online )
This project really showcases the power of open source and passionate people building something for the sheer joy of it :)...