Python License (CNRI Python License)

CNRI OPEN SOURCE LICENSE AGREEMENT

IMPORTANT: PLEASE READ THE FOLLOWING AGREEMENT CAREFULLY.

BY CLICKING ON "ACCEPT" WHERE INDICATED BELOW, OR BY COPYING, INSTALLING OR
OTHERWISE USING PYTHON 1.6, beta 1 SOFTWARE, YOU ARE DEEMED TO HAVE AGREED TO
THE TERMS AND CONDITIONS OF THIS LICENSE AGREEMENT.

If languages are defined by standards, what makes them open source? Well, the specification itself can be proprietary. You'll find in older main frame languages if you wanted the specifications you had to pay huge amounts of money for the detailed specifications.

The second opportunity is the implementation itself. For example with Ruby, there are several implementations, all of them happen to be open source.