The Gert VGA 666 (6 bits per colour channel, hence 666) is a breakout/add on board for the Raspberry Pi. It is an open source hardware design released publicly by Gert van Loo.
It is a neat and very useful solution for using a VGA screen/monitor with your Raspberry Pi and is far cheaper than an HDMI to VGA adapter or similar. The VGA connection is driven natively in hardware over the GPIO pins (using a parallel interface) and uses around the same CPU load as the HDMI connection on board. It is capable of displaying 1080p60 VGA video with no CPU load.