I got these ultra-cute little ESP-32-C3 micros the other day, they have teeny tiny 0.42" OLED displays built in, fantastic for putting a little sensor data or debugging info on. This is written on the Rust for ESP32 ESP-HAL using the embedded_graphics library.
That's a USB-C cable it's plugged into, for scale. You sacrifice some IO on this model but my plan is to use this to talk to my little air-quality sensor and have it report back to a server somewhere. This board takes battery power but I don't think it has battery management, I'll need to see how that works. I have lipo chargers lying around.
These are also the first RISC-V processors I've programmed. Fortunately as the guy who was my boss for like three months one time told me, you mostly don't need to care what the underlying architecture is unless you're doing really heavily optimized code or writing compilers. The ESP-RS project also works for the older Xtensa chips, which is handy especially because some of those are dual-core.
Unfortunately I've had trouble getting ESP-IDF-HAL to work, which is what you need to talk to the wi-fi side of things, but that is probably just me being absentminded somewhere. I'll figure it out, without wi-fi the ESP32's are much less interesting. There is an experimental wifi library for this HAL but if you're going to be doing networking you probably want the stdlib on your side anyway.
