Version 1 of the license didn't make sense: it required a Spine license to use the Spine Runtimes at all. This means if you used the Spine Runtimes in your application, anyone who purchased a copy of your application also needed a Spine license to use the runtimes. This was not the intent!
Version 2 of the license fixes this by allowing anyone to use the Spine Runtimes but only for internal use. When you purchase Spine, the Spine license (http://esotericsoftware.com/spine/files/license.txt) grants you the right to make and distribute derivative works of the Spine Runtimes. Now it makes sense: making and distributing applications with the Spine Runtimes requires a Spine license, but anyone can run that software without needing a Spine license.
With this fixed, I hope we never need to change the license again!
Changed from New BSD to a custom license. The new license requires a Spine license to use the code. If you have a valid Spine license, you can do whatever you like with the code. This should not be a problem for anyone using the runtimes with Spine, nothing changes. If using the runtimes without a Spine license, you now need a Spine license. This is because the runtimes were created explicitly to be used with Spine.
