Affiliate system allow affiliates to earn a profit through purchases/subscription made by their clients. It encourages your members to share and introduce your website to others. It is a perfect tool to track referrals to your website.
Badges plugin encourages members to perform various activity, frequently interact with each other and compete with friends in your social network. It is a simple and fun way to increase interaction and reward member activities. You can create different badges and define conditions to get them, for instance 30 blog posts to get Super Blogger badge and 10 music tracks for Music Lover badge. Badge can contain multiple conditions.