Educational Community License (ECL)
Apache 2.0 with a narrowed patent grant, written so universities would dare to contribute code.
Universities often hold large patent portfolios, and the Apache licence's patent clause worried their counsel: could a single employee's contribution accidentally license out patents belonging to an entirely different department of the same institution? ECL 2.0, approved by the OSI in 2007, is essentially Apache 2.0 word for word, but limits the patent grant to what concerns the individual contributor's own work.
It is used mainly by higher education's own shared projects, such as the Sakai learning platform and the Kuali administration suite. Outside that circle it is rare, and most people who spot it in a dependency list treat it as Apache with a footnote.