Pretty much everywhere you see a write up of Magento you see it referred to as an Open Source eCommerce platform.
The free community edition is indeed released under the Open Source License (3.0), but they also have two more comprehensive versions released under a Professional and Enterprise name
In order to contribute code to the SVN repository then “only team developers/coders are eligible to contribute changes directly to repository" (http://www.magentocommerce.com/boards/viewthread/15608/#t54063)
Okay, so that in itself is quite common in Open Source projects but as of autumn 2009 they brought in the Magento Contributor Agreement which all contributors have to sign if they want to get involved (http://www.magentocommerce.com/blog/tomorrow-today/), an extract from which reads:
You hereby grant to us a perpetual, irrevocable, non-exclusive, worldwide, nocharge, royalty-free patent license to: make, have made, use, sell, offer to sell, import, and otherwise transfer your contribution in whole or in part and derivative works thereof.
Which has nothing to do with Open Source principles.
I've put the development process into a diagram as so:
If you look at how they are comparing their different products that they are claiming that all three versions are built using the "Open Source Development Model": http://www.magentocommerce.com/product/compare
As far as I'm concerned, the Magento Contributor Agreement is not an Open Source development model. What do others think? Is there anybody here that contributes code to Magento?
(I've put a number of questions about this on the Magento forum but they remain unanswered.)