RSS 1.1: RDF Site Summary (DRAFT) - how sensible. Someone designed an update to RSS 1.0 (yes, that unloved RDF-based format that hardly anyone really knows). Because, there aren't enough feed formats yet, so you definitely have to add one more.
Along those lines, I also stumbled upon the HTML Syndication Format - another thing like that, where someone thought it would be a good idea to deliver the feed as specially tagged XHTML source.
And unlike RSS 3.0 (which is based on YAML instead of XML), the other two seem to be more or less serious (with the HTML Syndication Format I'm still hoping it was just an elaborate April Fools' joke ...)