The Parity Public License
Parity is a public
LICENSE for open software that requires users who build with your software to share their work with the community, too. In other words, Parity makes your work free for open source, like GitHub, Travis CI, and other current-generation services.
You might choose Parity because you're a pragmatic idealist looking for a copyleft license that's evolved with the times.
You might choose Parity because you're realistic about the need for financial support for your work, and want to sell licenses to users who won't give back in kind.
You might choose Parity because it's particularly important to make sure your users can understand your license.
Parity improves on previous strong-copyleft licenses in several ways.
Parity makes an effective share-alike deal with users of your software, whether your software happens to be a library, a developer tool, or a complete application. The ASP, private-changes, and developer-tools loopholes in licenses like GPL and AGPL have all been closed.
Parity is written to be read, in plain language, with a simple "here's your permission, and here are the rules" structure. The whole text of the license fits on a single piece of paper, with lots of room to spare.
Like other share-alike licenses, Parity differs from MIT, BSD, Apache 2.0, and other pure-permissive licenses by requiring users to share software back to the community.