Are you confused about the difference between PubSubHubbub and rssCloud? You're not alone.
Here's how the confusion came about:
Dave Winer invented rssCloud way back in the day. It only distributed lite pings, the callback endpoint was the IP address that you subscribed from, and nobody really ever implemented it, so you probably never heard of it. We sure hadn't.
Fast forward 5 or 6 years. Brett Slatkin and I want to fix the polling problem and we're annoyed that all companies seem to have an internal pubsub system, but none of them work on the Internet, and XEP-0060 just isn't getting adopted, probably because XMPP weirds people out. We start sketching out PubSubHubbub. From day 1 we do all development in the open, on pubsubhubbub.googlecode.com. Initially we only target Atom for simplicity until we got a prototype working. We work on PSHB for about a year, during which time we hear about rssCloud and are impressed at the foresight but reject it as not satisfying our design goals. After a year of working on PSHB, we demo it at the "TechCrunch Real-time Stream Crunch-Up" event. We add RSS support a few days before the event because it's trivial at that point. It's unfortunate that both Atom and RSS exist, but that's reality, so we support both.
Right after we present, we get a request to call Dave Winer. He wants to "do voice", so Brett and I hop on our cellphones and the three of us have a conference call, with Brett and I outside on the street trying to find places to stand with less road noise. Over the next 15-30 minutes, we slowly walk him through PubSubHubbub, repeatedly, explaining why webhooks and fat pings are important (no thundering herds DoSing publishers!), explain all of our design goals (pushing complexity to the hub, keeping publishing simple, decentralized, using HTTP, etc, etc...)
Dave Winer writes an article praising PubSubHubbub. Great!
Dave Winer reads the PSHB spec and notices it still says "Atom only, not RSS". Shit. We forgot to update the spec after we added RSS support.
Perhaps due to our RSS documentation omission, or perhaps because he realized pubsub was finally in vogue, he's now gone and dusted-off and augmented his old rssCloud protocol that's RSS-centric.
The arguments in favor of rssCloud go something like this: 'we can't have BigCo control the spec. We should have an independent spec!' Or, in his words: "Google sux". To reply to that specifically: This isn't even a Google-initiated project --- it's Brett & my 20% (or 5%?) time project, trying to fix something we find annoying on the web. We've been transparently working on this in the open from day 1. Yes, we happen to be Google employees. We have no internal docs or project plan on this. If Dave wants something different, he's just as welcome on our mailing list as everybody else (many individuals and companies, working together to build consensus....). Instead, he's heavily promoting the largely-unchanged rssCloud and not wanting feedback. Seems silly, but that's that.
Unlike rssCloud, which Winer says is frozen and a "done deal", the Hubbub protocol isn't frozen. It's in development so far as we'll make changes and additions that are good and useful, and try hard not to break backwards compatibility (especially on pinging). We have a few major things yet mostly untackled (including distribution of private content). The rssCloud mailing list says "This is a mail list not a standards body". If you'd like to work on a standard, join the PSHB mailing list.
Some of the good articles on the technical differences between the two protocols:
Anyway, I apologize for all the confusion. I feel like had we only promoted RSS more heavily in the 0.1 draft of the spec, I wouldn't be writing this blog post today.
Hopefully this is the last I'm going to say on this topic. Back to doing productive things....