Tim Berners-Lee had invented the World Wide Web in 1989, but for its first few years it was mostly text, used by physicists and computer scientists. What turned it into something everyone would use was a browser: Mosaic, released in 1993 by a team at the US National Center for Supercomputing Applications, including a young Marc Andreessen.
Why it mattered
Mosaic did two things that mattered enormously. It displayed images inline with text — so a web page could look like a printed page rather than a terminal — and it was easy to install on the ordinary Windows and Mac computers people already owned.
Suddenly the web was visual, friendly and within reach of non-experts, and its growth became explosive. Andreessen went on to co-found Netscape, whose browser lit the fuse of the dot-com boom and triggered the "browser wars" with Microsoft's Internet Explorer. Nearly every browser since — Firefox, Chrome, Safari, Edge — descends from the moment Mosaic made the web something you could simply look at.