As per Drupal.SE's Birthday Celebration, I was thinking of a contest to reward the participation on the site during a week (from now on, the contest week). A prize would be given in the following cases:
For all the users: The reputation they gained during the contest week is at least 600, and it is the double of the reputation they gained in the 7 days before the contest week. The reputation gained for posts created more than 7 days before the contest week are not taken into consideration.
For the users whose reputation is still 1 or 101 at the beginning of the contest week: Their reputation increased of at least 300, and they answered at least 5 questions.
For all the users: Between 7 days before the contest week, and the end of the contest week, they answered to at least 56 questions, and each answer has got, during the contest week, a score of at least 3, and no more than a down-vote.
For the users whose reputation is still 1 or 101 at the beginning of the contest week: Between 7 days before the contest week, and the end of the contest week, they answered at least 28 questions, and each answer has got, during the birthday week, a score of at least 2, and no more than a down-vote.
For users who have never flagged a post before the contest week starts: They flagged at least 30 posts, and not more than a quarter of their flag was declined.
For users who have never voted to close a question, or flagged a question to close it, before the contest week starts: They voted to close at least 30 questions, and at least three quarters of the voted questions was closed.
For the users who have already voted to close a question: They were the first users to vote to close 70 questions that were then closed.
For users who have never suggested an edit before the contest week starts: They suggested at least 70 edits, and not more than a quarter was rejected.
For users who has never offered a bounty when the context week starts: They offered 3 bounties, for a total bounty of at least 300, and they assigned all the bounties after at least 5 days the bounty was started.
The purpose of the contest is incentivizing the general activity on the main site. It is not offering something already given from badges, and that is the main reason the contest tasks are different from the requirements of any badge. Also, the prize for any of the contest task is not a badge.
The prizes will be decided from Stack Exchange. :-)