STM Nucleo F103 boards - Shtucer/Arduino_STM32 GitHub Wiki
The repo now contains provisional support for the STM Nucleo F103RB
This is currently a work in progress by Matthias on the Arduino forum
Currently only GPIO is known to definitely work, however Serial 1 should redirect to the virtual com port that is part of the Nucleo drivers package.
Upload is via the STLink co-processor on the Nucleo board.