Who first used computers?

Answer 1

Some of the first computers were used to weave things automatically by having a series of holes that a machine interpreted into a pattern. Later computers made other items. Some pianos can play music when you put in a cylinder with holes or bumps that the play a song on the piano.

Answer 2

There are several claimants for the title of "first computer." Also, the designers will be listed rather than the "users", since that information is easier to find (also, presumably the designers WERE the first users).

Charles Babbage is generally credited with the design of the first (mechanical) computer, which he called a "Difference Engine". Why it wasn't "really a computer": he designed it and did some preliminary studies, but never actually built it. When one was eventually constructed to his design, it did work as intended, though this was not done until well after electronic computers were in widespread use.

The German Z3 (May 1941) was designed by Konrade Zuse. Why it wasn't "really a computer": though programmable, it wasn't fully electronic; it used relays for storage and was therefore partly mechanical in nature. Also (and probably more importantly), it lacked conditional branching.

The Atanasoff-Berry Computer (summer 1941 or 1942, depending on what source you believe) was designed by John Atanasoff and Clifford Berry. Why it wasn't "really a computer": though fully electronic, it wasn't programmable and could only be used for one specific task (solving linear equations).

Colossus (1943) designed by Tommy Flowers during WW2 for the decoding of German codes. Why it wasn't "really a computer": digital, fully electronic, and programmable to some extent, it was still a special-purpose machine designed specifically for codebreaking and couldn't be used for general calculations.

Harvard Mark I (1944) designed by Howard Aiken: essentially the same issues as the Z3.

ENIAC (Feb 1946) was really the first machine that was clearly an electronic, Turing-complete, programmable general-purpose computer with no quibbles (well... "programming" it did involve physically moving wires around; however, it was designed so that this could be done relatively easily). It was designed primarily by John Mauchly and Presper Eckert with a team of others working on specific portions.