An important part of Drupal is its open source licence. This has some important implications:
- Anyone who has the Drupal software (or plugins) to use Drupal, study the code it is built of, share the code with others, and modify and improve the code. Also, if sharing the Drupal code - or derivatives - the code must be shared under open source licence.
- Since it is up for anyone to share open source software, there are rarely any purchase or licence fees for the code itself. Downloading and starting to use Drupal doesn't cost a penny.
- There are, however, costs associated with getting professional support or hiring developers for a project. (There are Drupal shops of varying sizes providing professional support, all over the globe.)
- Like many open source projectss, Drupal is being developed as a collaborative project between many, many participants. More than a thousand developers contributed to the code in Drupal 7 core, and hundereds of thousands of people contribute in one way or another to the project.
In this screencasts, it is also mentioned that we don't have any formal certification for Drupal developers - and why we don't have that.