What type of plugin do you need?
I'll follow up with you by email, but since you asked, I guess I'll give more specifics here...
I have a separate MySQL database (not the RC database) where each user has multiple lists of other users. I want the plugin to fetch the lists for the logged in user from this separate database and present these lists as multiple address books. I also want the vCards for each address in the books to be stored/fetched from the separate database. These address books and vCards should be read-only and should be searchable just like the Personal Addresses would be (I don't need the Personal Addresses lists at all. The only addresses my users can send to are the ones in the read-only address books that the plugin manages.).
My site will have a forum that I will use for creating accounts and allow the users to manage their profiles/identities. I don't need help on the forum side (or the Postfix/Dovecot side), but I'd also like help in implementing code to create the RC identities from the user's registration data when they register (identity data would need to be read-only by the RC users and only changed through the forum software). I also want the forum profile data to be turned into vCards that the RC plugin would use for showing a contact. Basically, the forum will be the way the users will manage their identities/profiles/address books.
I've looked at several address book/contacts lists plugins and I don't think this job will be that hard for someone that is very experienced with how RC works. I would program it myself, but I don't really want to take the time to learn RC plugin programming. I can code the changes I need to the forum side myself (since I know the forum software already) but I am looking for help in organizing the forum data in a way that RC can best understand (even if that means having the forum side do the updates to the RC database directly - like creating identities and vCards).
I also need the programmer to know vCard format and what kind of data I can stuff into the vCards (and how to format it) so that other Contact List managers (not just RC) can import the vCards.
