The following come to my mind: - Google Earth: A globe with ultra-zoom just didn't exist before. - Tex and LaTeX: They revolutionized Academic typesetting and

The following come to my mind: - Google Earth: A globe with ultra-zoom just didn't exist before. - Tex and LaTeX: They revolutionized Academic typesetting and publishing. - DAWs: I used to use a four-track recorder. When I first got to edit in a DAW with a few built-in effects, that was such a quantum leap. (I was about to write "affordable DAWs" but to be honest these came quite late and my first DAW was a cracked copy of Protools, of course.) - REALBasic when it was affordable shareware: I've never been more productive than in REALBasic. (Also learned my lesson, though, never rely on commercial tools whose price suddenly might skyrocket.) - XLisp: I did not end up programming much in it but this was so good and mature software for hobby programmers interested in Lisp during the 90s (at a time when CommonLisp was hard to get outside your university). - Wikipedia: Doesn't really count as software but I had to include it. It's possibly the most useful Internet-based tool besides email.