> With CC0, you relinquish all rights to the work, including copyright.
With CC0, you relinquish your copyright only, but explicitly retain trademark and patent rights (!).
> 4. Limitations and Disclaimers.
> a. No trademark or patent rights held by Affirmer are waived, abandoned, surrendered, licensed or otherwise affected by this document.
This makes it sort of iffy for software when software patents exist unless coupled with some kind of patent waiver or assertion of not holding and not being aware of patents. While you can argue with MIT-0/0BSD/whatever else there might be that there is an implied patent license, there is an explicit non-license for patents with CC0.
[0] https://bytes.grubhub.com/why-we-use-crypto-when-generating-...