ShareAlike
Two of the licenses (BY-SA and BY-NC-SA) require that if adaptations of the licensed work are shared, they must be made available under the same or a compatible license. For ShareAlike purposes, the list of compatible licenses is short. It includes later versions of the same license (e .g., BY-SA 4.0 is compatible with BY-SA 3.0) and a few non-CC licenses designated as compatible by Creative Commons (e. g., the Free Art License). You can read more about this at the CC wiki ShareAlike Compatibility page, licensed CC BY 4.0, available at https://wiki.creativecommons.org/wiki/ShareAlike_compatibility, but the most important thing to remember is that ShareAlike requires that if you share your adaptation, you must do so using the same or a compatible license.
Public Domain
In addition to the CC license suite, Creative Commons also has an option for creators who want to take a “no rights reserved” approach and disclaim copyright entirely. This is CC0, the Public Domain Dedication tool.
Like the CC licenses, CC0 (read “CC Zero”) uses the three-layer design—legal code, deed, and metadata. The CC0 legal code itself uses a three-pronged legal approach. The first approach is for the creator to simply waive all of their rights to the work. But some countries do not allow creators to dedicate their work to the public domain through a waiver or abandonment of their rights, so CC0 includes a “fallback” license that allows anyone in the world to do anything with the work unconditionally. The fallback license comes into play when the waiver fails for any reason. And finally, in the rare instance that both the waiver and the “fallback” license are not enforceable, CC includes a promise by the person applying CC0 to their work that they will not assert copyright against reusers in a manner that interferes with their stated intention of surrendering all rights in the work.
Like the licenses, CC0 is a copyright tool, but it also covers a few additional rights beyond those covered by the CC licenses, such as noncompetition laws. From a reuse perspective, there still may be other rights that require clearance separately, such as trademark and patent rights, and third-party rights in the work, such as publicity or privacy rights.
