Punjab is a HTTP jabber client interface. It is a SOAP, XMLRPC, XEP-0025 or XEP-0124 server that allows persistent client connections to a jabber server. It can be used for many things, but its main purpose is to allow for stateless applications (ie web) a stateful connection to jabber.
let enter the BOSH era
Pubsub nodes are organized in a hierarchical tree, similar to a file system. mod_pubsub imposes a special structure on this tree. There is a special node, pubsub/nodes, that contains all other created nodes. Nodes of users have names like home/server/username/whatever. If you try to create a node whose name doesn't fit that pattern, you will get an error. If you don't specify a name (i.e. create an instant node), the server generates a name that fits this pattern
Some says that it's the future of feeds, at least server-to-server subscriptions.