Check out this infographic for a great summary!
Source and original infographic in PDF: http://mogdesign.eu/blog/downloads/drupal_infographics.pdf [4]
Links:
[1] http://linux.philosweb.com/drupal/category/it/drupal
[2] http://linux.philosweb.com/drupal/category/it/open-source-foss
[3] http://linux.philosweb.com/drupal/category/it/visualization
[4] http://mogdesign.eu/blog/downloads/drupal_infographics.pdf