Most boards in this category come equipped with Digital Inputs, Digital Outputs, and/or Analog Inputs, making them central pieces of many Phidgets systems. For example, an InterfaceKit with a number of Analog Inputs could be used to read data in from several different sensors and send this data to a program on your computer to be used in real-time calculations.
In addition to these input and output ports, many of these boards have a special feature or add-on that sets it apart from the rest, like a USB hub, an LCD screen, or even a built in computer to run your program without being plugged into a USB port.
Some boards in this category perform a specific function instead of having the versatility of generic inputs and outputs. For example, the PhidgetFrequencyCounter counts the frequency of electrical pulses on its input, usually from certain specialized sensors.