Automatic Usergroup Assignment during registration
 

I've been looking, to no avail, for a plugin that would automatically assign new members into one of several usergroups. I want to balance the assignment evenly between the usergroups when people register.

Here's the scenario:

Three usergroups exist: Project A, Project B, Project C

User signs up and is automatically assigned to Project A Usergroup.
Second user signs up and is automatically assigned to Project B Usergroup.
Third user signs up and is automatically assigned to Project C Usergroup.
Fouth user signs up and is automatically assigned to Project A Usergroup.

Rinse... Repeat...

Is anyone aware of any mods or products/plugins that can accomplish this? Additional functionality that would be nice would be calculation of the number of members in each usergroup. If each usergroup has 10 members and four are pulled out of Group A and assigned to Group C, this would leave A with 6, B with 10 and C with 14. At this point the product would only assign new members to A and B until they all had 14 users and then proceed with the normal rotation logic as defined above.

Any information/help/direction would be most appreciated!

Regards,