When programmers on the Internet can read, redistribute, and modify the source for a piece of software, it evolves.
People improve it, people adapt it, people fix bugs.
This can happen at a speed that, if one is used to the slow pace of conventional software development, seems astonishing. There are a wide variety of Open Source projects, in various stages of development, all with their own unique cultures. Find a project that interests you and join in. I promise it will be a valuable experience. Open Source projects which interest me Zope - Z Object Publishing Environment is a very flexible application server.