If you own a device that has the CH340 or CH341 USB to Serial chip to communicate with your mac and after updating to version 10.11.2 (El Capitan) your board is suddenly not detected, please download the updated drivers.
This chip is quite common in cheap Chinese Arduino Nano and Uno clones. Since June 2015, in collaboration with WCH, the manufacturer of the chip, we were the first worldwide to offer drivers that were working with OSX Yosemite and later El Capitain. The update of El Capitan to 10.11.2 broke the previously offered drivers.
The drivers now available work in all OSX versions starting from 10.6.