If you ask the average geek worth his salt what was the killer app that launched the microcomputer revolution the answer would probably be "Visicalc, of course!"
I take issue with this answer. Long before the spreadsheet application Visicalc was a gleam in Dan Bricklin's eye the most important and powerful application for small computers was the BASIC programming language. Without Microsoft BASIC (and this is Microsoft's real and lasting legacy if you ask me) very few people would have been able to do anything useful with computers. Most versions of BASIC back then were variations on Bill Gates' original BASIC interpreter.
Without BASIC we would not have seen so many kids grow up to be programmers, myself included. This is the very reason why I work on BASIC language products because I believe that there's no good reason why anyone with a little desire and time shouldn't be able to create software.
Run BASIC is very much in the same spirit as the early BASIC, but for the web. Now anyone can create web applications. :-)
Run BASIC - Killer app for the Internet age!