Schematics and CAD files: Creative Commons Attribution Share-Alike
“ Arduino” is trademarked, and official third-party Arduino products are licensed.
Active forums, wiki, etc.
Culture of shared code and schematics, peer support.
Companies/designers that use Arduino often (but not always) create open source products.
Boards or projects based on Arduino usually have names that refer to Arduino (Boarduino, Stickduino, Sanguino, etc.)
How is Arduino Open Source?
Arduino Lilypad, Leah Buechley & Sparkfun Electronics Arduino Mega, Arduino Arduino Nano, Gravitech Arduino Single-Sided Serial Board, v. 3 Adilson Akashi Arduino Pro and Pro Mini, Sparkfun Electronics Arduino Duemilanove, Arduino Some Official Arduino Products
What and Who Commercial and Non-Commercial Arduino Shields & peripherals Project & product dev Education & publishing Consulting Software and IDE design & support Boards Arduino team Manufacturers and distributors Universities and schools R&D departments Consultancies Artists, designers, engineers, inventors Hobbyists and students