stm32f042-hal
stm32f042-hal contains a hardware abstraction on top of the peripheral access API for the STMicro stm32f042 series microcontroller.
This crate relies on my stm32f042 crate to provide appropriate register definitions and implements a partial set of the embedded-hal traits.
Since this chip is very easy to use and put into your own boards I've developped quite a few boards with those chipped and often throw one in just for good measure. Hence I don't have any ready-made eval board I can recommend although there is a nucleo-f042k6 board on the market.
Some of the implementation was shamelessly adapted from the stm32f103xx-hal crate by Jorge Aparicio.