There are many ways to do a simple user interface. One is to use a simple character based LCD module. Most of these modules (sometimes available for less than 4$) feature a Hitachi HD44780 compatible interface. This card provides ease of connectivity to most of these available modules.
It also features the PCF8547 IO expander. In addition a AD5252 is used for TWI/I2C contrast control and backlight intensity control.