A license grants "outbound" rights to the user of of project. But the project does not give copyrights to the user.
A CLA enables a contributor to grant "inbound" rights to the project.
A CLA is a legal document in which you state you are entitled to contribute the code/documentation/translation to the project you’re contributing to and are willing to have it used in distributions and derivative works. This means that should there be any kind of legal issue in the future as to the origins and ownership of any particular piece of code, then that project has the necessary forms on file from the contributor(s) saying they were permitted to make this contribution.
The CLA also ensures that once you have provided a contribution, you cannot try to withdraw permission for its use at a later date. People and companies can therefore use that software, confident that they will not be asked to stop using pieces of the code at a later date.
A CLA is inbound, when a License is outbound.
Ideally, the inbound=outbound: the contributor give the same rights to the project that the project gives to the user. By default, if the contract does not define who will own the property, it is more likely than not that the person who wrote it will own it.
Two big families:
a Copyright Assignment Agreement (CAA), the contributor actually transfers copyright ownership of the contributions to the project, who can then license it however they want since they own it
can grant an irrevocable licence to allow the project maintainer to use the contribution.
As of August 2011, Canonical is requesting contributions be licensed under a Harmony Contribution Licence Agreement, rather than the copyright being assigned to Canonical. With the Harmony CLA, "the contributor gives Canonical a licence to use their contributions. The contributor continues to own the copyright in the contribution, with full rights to re-use, re-distribute, and continue modifying the contributed code, allowing them to also share that contribution with other projects."
All contributors of ideas, code, or documentation to any Apache projects complete, sign, and submit (via fax or email) an Individual Contributor License Agreement (ICLA). The purpose of this agreement is to clearly define the terms under which intellectual property has been contributed to the Project and thereby allow us to defend the project should there be a legal dispute regarding the software at some future time. A signed ICLA is required to be on file before an individual is given commit rights to a project.
Apache CLA : see here
CLAs twist the empowering, community-oriented, enjoyable experience of FLOSS contribution into an annoying exercise in pointless bureaucracy, which (if handled properly) requires a business-like, grating haggle between necessarily adverse parties.
Most projects use the same time-honored and successful mechanism used throughout the 35 year history of the Free Software community: submissions using the normal means to contribute to the project — such as patches to the mailing list or pull and merge requests — indicate the contributors' assent for inclusion of that Contribution in the canonical version under the project's license.
11. Patents.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.
It means that IP remains the Contributor by default.
Different use-cases:
Suggestion: