There are 3 additional devices that can be used with this board: 16-button scan-matrix keyboard, 128*64px small graphic LCD screen, 320*240px slightly bigger color TFT LCD screen. All of them are connected via pin header connectors. They make use of some of the pins dedicated to on-board buttons and 8-digit multiplexed 7-segment display. Conveniently, the keyboard is blocking the buttons it interferes with, and there is a switch that turns off 7-segment display in case one or both LCD screens (otherwise it would light random segments and be a distraction).

Below are photos of different configurations:

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Only Tang Nano 9k board is inserted into its place:

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With 4 by 4 scan matrix keyboard:

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With 128*64px graphical LCD:

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With 320*240px color LCD:

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And, to top it all, the board with all extensions installed:

In this maximal configuration it is possible for each addon, as well as bottom row of switches and bottom-right button to work together. The lcd screens are connected via SPI protocol, and use the same wire for data transfer, but each have dedicated pin for selection, so can be multiplexed. With all of this, the VGA monitor also can be connected and show independent image, as signals for it are on dedicated pins from 1.8V bank.