Is there any PHP (+ xml?) equivalent (or similar) for this awesome .net library?

[ZiNgA BuRgA]

Well you got your answer.

I seriously don't know why you want this though.  It's not popular or widely used, so mostly useless.
You seem to be highlighting the decentralised part a bit, and I don't think you fully understand what it really means...

If you just want to aggregate feeds for any particular purpose, you need to understand that each feed source needs to be using this, and I don't actually know any which do (that I'm aware of at least).  Otherwise, this doesn't work.