Retrocomputing is the use of older computer hardware and software in modern times. Retrocomputing is usually classed as a hobby and recreation.

Citizens band radio (also known as CB radio) is, in many countries, a system of short-distance radio communications between individuals typically on a selection of 40 channels within the 27 MHz (11 m) band.

Software-defined radio (SDR) is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software.