The Creative Commons Zero (CC0 1.0) license is the most liberal CC license. They place works in the public domain, and the author waives all copyright and related property rights worldwide, insofar as this is legally possible. However, patents or trademark rights of any party are expressly not affected by CC0, so it is possible to place patent-protected works under CC0.
Patents vs Open Source
In the 2000s, various companies, including Microsoft, tried to fight open source software via patent claims. In response, the Open Invention Network (OIN) emerged, whose members refrain from patent lawsuits against other members.
The open source world also saw the risk that companies might open source code protected by their own patents. If other developers use this code, they unknowingly put themselves at risk of patent lawsuits. Therefore, there is widespread agreement in the FOSS world that open source licenses must explicitly exclude the possibility of patent claims by the author.
The Fedora Project distinguishes between software, content, documentation, and font licenses in its list of approved licenses. CC0, previously listed there as an approved license for software and content, will only be allowed for content in the future. According to Fontana, it has not yet been clarified whether and how many program packages will be affected by this change.
