Unique reply counter

[JohnnieOO]

Anyone know of a mod that could be added to 3.6.8 that can count the total number of unique user replies to a post. In other words, I'd like to be able to track how many different users posted to every post started by each user. For example, User "a" starts 10 posts and each has 10 different UNIQUE user replies then he gets a score of 10*10=100. user "b" starts 10 posts and has 101 total replies, except, one of the replies is by "b" or a double reply by another user. Then his score is 101 minus the non-unique reply = 100.
Also, I'd like to be able to bracket this with dates. For example, I'd like to see which user created the most unique replies from Sept 1 to Sept 30.
The ultimate goal is to be able to run a monthly (or yearly or weekly) contest to:
(1) - determine who created the most traffic
(2) - have a lottery (for a prize) where all users are entered one time for each unique reply post.

Any known existing mods or anyone willing to create this one?

Thanks,
Johnnie