I just this week finished a project that has been hanging around for a while, mostly because it turned out to be much more work than I estimated. Earlier this year, I did some work using Nordic Semiconductor's nRF52840 ARM chip. Although the chip is nice, I didn't enjoy the software development experience using the tools that Nordic recommends, so I decided to do a "little" project to review some of the alternatives.
Turned out not to be so little, after all.
In any case, you can read the results on the project page. The highlights of the work were definitely learning about the Zephyr project and CircuitPython. I'm going to try to do some Rust stuff on the nRF52840 later to get an idea of how practical that is too, but I need a break from this stuff for a while first!