http://www.nearfuturelaboratory.com/2008/07/07/ds1803-digital-potentiometer/

Product page

This chip is a 8-bits port expander driven by SPI (or I2C for MCP23008 version).

Microchip MCP23S08 datasheet

This chip is a LED driver : this means you can connect up to 64 LEDs (matrix configuration), and drive them from a microcontroller via 3 lines. The chip has segments and digits lines. The digits sinks current, while the segments source. It also has built-in PWM to control the LED brigthness. See :

• max7219 datasheet
• Sample projects using the max7219.