EasyMock used to be under MIT license which seemed to be the simplest, freest and openest license there is. As per version 2.5.1, EasyMock is under Apache 2.0 license. BTW, versions 2.5 and 2.5.1 are identical except for the license.

Why do we changed?

It seems that the MIT license is in fact too open. It prevents some users to use EasyMock. Users with a law staff since us, naive engineers, are not aware MIT license put us under is such a threat.

In case you're interested, it's all about paragraph 3 of the Apache license.

3. Grant of Patent License. Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.

It basically means (correct me if I'm wrong) that the license grant a patent usage right to anyone using EasyMock if EasyMock code was ever patented. Which basically prevents us from building a successful open-source framework, have it used, patent it and ask money from our users.

However, it also means that no users can start a patent litigation lawsuit over EasyMock (the Work) without loosing the right to use EasyMock. So it also protects the contributors against weasels.

Objenesis and EasyMock CE will also be moved to Apache license for the same reason.