"Blue Pill" is a very cheap Maple Mini clone. Some features are improved:

  • 3.3v Power supply and VDDA improvements. 
  • USB ESD protection.
  • added USB reset circuit (not needed for some MCUs).
  •  Many Cortex M0, M3, M4 STM32 Microcontrolles may be mounted in this PCB layout. Check notes in schematic and read STM32 datasheets. 
  • external RTC oscillator is not implemented because no enought PCB spaces to follow STM design guide. ...I'll be pleased if anyone will find a solution