Some months ago there was a discussion about the licensing strategies of OpenERP, which released the server and the GTK client under AGPL and the web client under a somehow restricting license (can't remember exactly the restrictions, mainly branding, IIRC).
Can't find the link to the discussion in the archive now, since it's private (unfortunately) and the password reminder is not working. I recall someone talking about "open core strategy", since the web client is way better than GTK client.
I've just learned that since version 7 the GTK client has been discontinued and only the web client will be actively maintained and developed. Good news: it's released with AGPL (as the server), as far as I can see here:
http://bazaar.launchpad.net/~openerp/openerp-web/trunk/view/head:/LICENSE
Cheers, Federico