In his famous keynote at OSCON 2002, Lawrence Lessig talked about the "free culture" and the way "creativity and innovation always build on the past". The video is a must see for anyone working with or on Open-Source projects. Even if Lawrence does not talk explicitly about Open-Source in the first part of his talk, his arguments are still valid for Open-Source projects.
Symfony has been made possible because I was able to have a look at the code of other Open-Source projects. I was able to understand their code and adopt some of their ideas for symfony. Symfony would not have been possible without the work of thousands of developers before us. I get inspiration nearly everyday by reading code written by others in PHP, Python, Ruby, and even Java.
We have bundled third-party Open-Source projects like the Prado I18N librairies or the Propel ORM. We have converted code written in other languages to PHP, like the Ruby on Rails helpers. But most of the time, we have implemented our own solution based on the community experience. This is the case for the new form framework, for which I borrowed a lot of ideas from two Python projects: the Django framework and the formencode library. In symfony 2.0, we will have a Dependency Injection framework, inspired by the Java Spring framework. Instead of reinventing the wheel over and over again, we can build better tools thanks to existing ones.
Today, I am happy that our beloved symfony web debug toolbar has been ported to Django. This is the true spirit of Open-Source. In a world of competition, Open-Source projects are all about sharing code and experience.
Thanks to Open-Source, becoming a better developer is quite simple nowadays: read code written by others.