Metronome

A metronome is any device that produces regular, metrical ticks (beats, clicks) — settable in beats per minute. These ticks represent a fixed, regular aural pulse; some metronomes also include synchronized visual motion (e.g. pendulum-swing). The metronome dates from the early 9th century, Abbas ibn Firnas (810-887 AD), was patented by Johann Maelzel in 1815 as a tool for musicians, under the title "Instrument/Machine for the Improvement of all Musical Performance, called Metronome".^{[1] - As per Wikipedia}

Instead of buying the Hardware or Software for your Computer or Mobile, you could just type "Metronome" in Google search and Voila you have one Free of Cost :)