At the time, leaf labs offered its own customized Arduino IDE, and also something called "libmaple" which allows command line development. I began looking at an experimenting with libmaple in September of 2020. Overall I have been quite impressed. It is a superb resource for people working with the STM32F103 chip.
I started looking at the Arduino_STM32 project, but got fed up with tangles of include file dependencies. A simple command line makefile was also sorely missing. Then I discovered libmaple, and everyone has lived happily ever after.
"libmaple" came first, and has now been absorbed into the Arduino_STM32 project. Leaf Labs no longer supports libmaple, but is kind enough to keep various libmaple resources up on their web page. They are now offering engineering services rather than hardware. Good people.
Tom's Computer Info / firstname.lastname@example.org