USB serial console
The openSPOT3 shows up as a USB serial port (COM port) when plugged into a computer. You can reach the serial console by opening this USB serial port with serial terminal software like PuTTY, RealTerm, TeraTerm, minicom etc. To find out which is your openSPOT3's serial port device path (COM port number), look at the device list of your computer (in your operating system's control panel for example). You can use the following settings for opening the serial port, but in theory any configuration would work: baud rate 115200, 8 data bits, no parity bits, 1 stop bit.
The openSPOT3's serial console does not require drivers on modern operating systems, as it shows up as a standard USB ACM device with our official USB ID 0x1fc9:0x8125. You can download a driver for Windows XP, 7 and Vista here. Some users reported that Windows 8.1 also requires this driver, but it can only be installed if the signed driver requirement is turned off.
The serial console can be used to change basic network settings, reboot the openSPOT3, switch it to bootloader mode, see its debug log, reset the web interface password and many more. The list of available commands can be queried with the help command.