This recently released application lets you not only flash new binaries to any ESP8266 board using the FTDI, PL2303, CH34X and CP210X USB chipsets, but also offers a serial monitor for debugging ...

[Pete] was building a hot tub controller, using a WEMOS board based on the venerable ESP8266. After assembly, the board was plugged into USB and [Pete] hit the flash button. No dice. Investigation … ...