Wordpress User Sync across Multiple Installations

There’s already any plugin for wordpress that allow to sync the user data across different wordpress installations or anyone here is able to develop it?

What I’m needing is a plugin to sync the user accounts on the Master website to the slaves websites. This website do not share the database and are from different companies.

To be more specific, what I want it’s that slaves webistes sync automatically the user data from the master website or at least, request this data to the master website (without being installed in the same database).

Basically, make the master wordpress installation a Authentication Provider for the other websites. Through an API would be perfect. Ex. The master website creates the API auth code and a Secret code for the client website (like facebook or twitter apps have), then the client website request the confirmation or the info of the user’s data using this API keys.

The usage of Wordpress MU or the same database option it’s not reliable for what I want. This because some of the website are already MU installations and do not share the same database. What I want is integrate a universal login for the entire and independent (databases) network of websites that I have now.

As far as I know, there is no existing plugin here in CodeCanyon that would suffice the features you needed.

i can code it for you, let me know if you’re interested