There are and were many other video posting apps before youtube came but youtube is still the most popular video posting site today.<p>What made it so popular?
I remember getting into youtube because it was a great place to watch TV shows. I remember staying on youtube because people (the youtube Community) were uploading interesting and relevant videos. As a place for random lolcats and funny videos, I don't think youtube is anything more than a huge personal library that happens to also be public so you can share it with your friends..
Web videos used to be in QuickTime, Windows Media, Real Video, etc. It was a mess to deal with all of those formats, plus the videos would play in an external application.<p>YouTube popularized Flash-based video, which could play directly in the browser. It's ironic now since the rage is HTML5 and getting away from Flash...