Are there any good computer programs you can buy or get for free to run sites similar to Facebook or piratebay?

[feynman_rocks]

These are all unrelated questions, but I'll try:

1. Yes. Many are free. What you're looking for is a CMS (content management system). These come in all different flavors, really popular ones these days seem to be Drupal or Joomla. The secret sauce in most of these is that they integrate databases into a website front end so that you can store and manage a dynamic website. It really depends on your background how easy these are to get going.

2. BitTorrent. All the ones you mention use the bittorrent protocol. If you understand how bittorrent works, then you'll kinda see how this hooks into point #1.

3. Like I said, as your skill level goes up, the cost goes down (because you can do it yourself with free/open source tools). With, I would say, a few months work, all this can be done for free. Hosting is a different matter.