A brief bit of research. Links are here.
Part of the usual end of year house cleaning.
It can also be found here.
Really Simple Discovery (RSD) is an XML format and a publishing convention for making services exposed by blog, or other web software, discoverable by client software. It reduces the information required to set up editing/blogging software to a minimum.
Repository here: Really Simple Discovery
Attention. These are not... oh to hell with it.