I needed a simple, easy to work with, asyncronous safe RSS parser.  I tried TclRSS [http://nul.jp/2003/tclrss/], but it had heavy requirements, and I never actually figured out the correct combination of dependencies and their versions needed to make it work.  I gave up on that and started writing my own RSS parser, using the subset of the TclRSS API that I had already written a program to.  I found [TAX] a small, good-enough Tcl XML parser and wrote an RSS parser from example RSS 2.0 feeds, and not from the specification (I was in a hurry).  It works with my limited testing (digg.com, sourceforge, and cnn), but probably doesn't work for anything that is not exactly RSS 2.0 and pretty close to one of my examples.

 #! /usr/bin/env tclsh
 
 package require tax
 
 namespace eval rss {
 	namespace eval channels {
 	}
 	namespace eval items {
 	}
 }
 
 proc rss::__replace_entities {text} {
 	return [string map [list "&gt;" ">" "&lt;" "<" "&amp;" "&"] $text]
 }
 
 proc rss::__strip_html {text} {
 	return [regsub -all -- {<[^>]*>} $text ""]
 }
 
 proc rss::__tax_add_to_object {obj tag isClose isSelfClosing properties body} {
 	upvar #0 $obj rssobj
 	set channelid [namespace tail $obj]
 
 	set tag [string tolower [string trim $tag]]
 	if {$tag == "docstart"} {
 		set rssobj(parent) [list] 
 
 		namespace eval ::rss::items::$channelid {}
 	}
 	if {$tag == "docstart" || $tag == "rss"} {
 		return
 	}
 	if {[string index $tag 0] == "?"} {
 		return
 	}
 
 	if {$isClose && !$isSelfClosing} {
 		if {$tag == "item"} {
 			# We close tag items twice, because we add a fake open with the tag id
 			set rssobj(parent) [lrange $rssobj(parent) 0 end-1]
 		}
 		set rssobj(parent) [lrange $rssobj(parent) 0 end-1]
 		return
 	}
 
 	lappend rssobj(parent) $tag
 
 	set parent [lindex $rssobj(parent) end-1]
 	switch -- $tag {
 		"item" {
 			if {$parent == "channel"} {
 				set lastusedid [namespace tail [lindex [lsort -dictionary -decreasing [info procs ::rss::items::${channelid}::*]] 0]]
 				if {$lastusedid == ""} {
 					set lastusedid 0
 				}
 				set id "::rss::items::${channelid}::[expr $lastusedid + 1]"
 
 				proc $id [list command [list obj $obj] [list id $id]] {
 					upvar #0 $obj rssobj
 					switch -- [string tolower $command] {
 						"title" {
 							set idx [list $id title]
 						}
 						"link" {
 							set idx [list $id link]
 						}
 						"description" {
 							set idx [list $id description]
 						}
 						"date" {
 							set idx [list $id pubdate]
 						}
 					}
 
 					if {![info exists idx]} {
 						return ""
 					}
 					if {![info exists rssobj($idx)]} {
 						return ""
 					}
 
 					return $rssobj($idx)
 				}
 
 				lappend rssobj(items) $id
 
 				lappend rssobj(parent) $id
 			}
 		}
 		"title" {
 			set rssobj([list $parent title]) [__strip_html [__replace_entities $body]]
 		}
 		"link" {
 			set rssobj([list $parent link]) [__replace_entities $body]
 		}
 		"description" {
 			set rssobj([list $parent description]) [__strip_html [__replace_entities $body]]
 		}
 		"pubdate" {
 			catch {
 				set body [clock scan $body]
 			}
 			set rssobj([list $parent pubdate]) $body
 		}
 	}
 
 	if {$isClose} {
 		# For self-closing tags
 		if {$tag == "item"} {
 			# We close tag items twice, because we add a fake open with the tag id
 			set rssobj(parent) [lrange $rssobj(parent) 0 end-1]
 		}
 		set rssobj(parent) [lrange $rssobj(parent) 0 end-1]
 	}
 
 	return
 }
 
 # Return ID
 proc rss::parse {data} {
 	set lastusedid [namespace tail [lindex [lsort -dictionary -decreasing [info vars ::rss::channels::*]] 0]]
 	if {$lastusedid == ""} {
 		set lastusedid 0
 	}
 	set id "::rss::channels::[expr $lastusedid + 1]"
 
 	upvar #0 $id rssobj
 
 	tax::parse [list ::rss::__tax_add_to_object $id] $data
 
 	proc $id [list command [list obj $id]] {
 		upvar #0 $obj rssobj
 		switch -- $command {
 			"items" {
 				set idx items
 			}
 			"description" {
 				set idx [list channel description]
 			}
 			"link" {
 				set idx [list channel link]
 			}
 		}
 
 		if {![info exists idx]} {
 			return ""
 		}
 		if {![info exists rssobj($idx)]} {
 			return ""
 		}
 		return $rssobj($idx)
 	}
 
 	return $id
 }
 
 proc rss::cleanup {id} {
 	if {[string match "::rss::channels::*" $id]} {
 		set channelid [namespace tail $id]
 		foreach proc [info procs ::rss::items::${channelid}::*] {
 			rename $proc ""
 		}
 		unset -nocomplain $id
 	}
 
 	return 1
 }
 
 package provide rss 0.1

You'll notice that it is slightly inconsisent towards the middle.. I should have used a namespace under ::rss for both channels and items, but I didn't realize this until I didn't feel like changing it.  Feel free to edit the above, or use it in your own code.