Need private message plugin for user

hi

I need a plugin which allows wordpress users to exchange private message. Sort of the system existing in forums.
I saw such plugin for an old version of WordPress (no updates, not working) and for wordpress forums (inconvenient to use with blog).
Would a guru please consider writing such plugin? It would be great then to create an additional role, such as User, so that a person using the private messaging feature won’t automatically subscribe to blog posts.