A unique aspect of Rejecta Mathematica is that each paper will be published together with an open letter from the authors discussing the paper's original review process, disclosing any known flaws in the paper and stating the case for the paper's value to the community.
Rejecta Mathematica is a new, open access, online journal that publishes only papers that have been rejected from peer-reviewed journals (or conferences with comparable review standards) in the mathematical sciences.
Is this a joke? This and other natural questions are discussed here. In case you wonder who the editors of this journal are, look here.
I am looking forward to seeing what papers will appear in the first volume of the journal :-)