USB Serial for Blue Pill (STM32) with PlatformIO - Donney Fan
Use Android to Flash STM32 BigClown Modules - Hackster.io
Programming an STM32F103 board using its USB port (Blue Pill) | by Param Aggarwal | Medium
STM32 - RevSpace
GitHub - DAlexis/stm32-usb-bootloader: This repository contains bootloader for stm32f1xx microcontrollers. It works for stm32f103ret6, but you can simply adopt it to any MCU supporting STM32 HAL library with USB and SD-card
STM32 Clones: The Good, The Bad And The Ugly | Hackaday