I've been working on a WildFire / Openfire based IM application, and so far its been acting good.
A few things pointers:
1. Wildfire / Openfire are pretty popular OS jabber servers out there
2. Flash libraries include - XIFF from JiveSoft, and
mx.collaborations.xmpp package, by Danny Dura of adobe. Not sure if there are more.
A few things to remember:
1. I've heard from my network folks that Openfire/Wildfire is not 'scalable', so not very future proof.
2. Openfire/Wildfire work over xmlsockets - which might get blocked at firewalls. An answer to this is BOSH ( or HTTP Binding) and Openfire doesnt support it natively
3. you can install BOSH support as a component over wildfire/openfire. Google for BOSH and Punjab ( thats the name of the BOSH component)
Haven't used Red5, have heard its pretty good, but not sure especially since its still in early stages of development.
~Arul Prasad.
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Arul Prasad
http://arulprasad.blogspot.com