The invention of the printing press in the 15th century by Gutenberg was one of the most revolutionary outcomes of technology. I'd say it stood above the invention of the personal computer at least initially for it brought a means of communication to millions all over Europe.
Johannes Gutenberg was a German goldsmith' who probably had no idea of how far reaching his invention of pressing ink onto a rolling pad was going to be. Before this, i.e. 1450, books were produced by scribes who laboriously copied everything by hand, whole books at a go.
No matter how hard and diligently they worked, their production meant that books were very few and limited to the very rich or the church, which came to the same thing. After the printing press, peasants could become literate if they had access to pamphlets and a tutor, such as a monk. Printed matter, literature conveyed to millions, was a key part of the Renaissance.