With BuddyPress Rate Forum Posts plugin your BuddyPress site memebrs can rate forum posts. It highlights good posts whereas poor posts are diminished. Highlighted karma points are visible for each site member. Note: The plugin is only for group forums, it is yet not compatible with BuddyPress site wide forums feature.
CubePoints is a free point management system for WordPress website users. This plugin lets you give your website visitors virtual credits on the basis of posting comments, creating new posts and even by logging in each day to your website, after gathering more points you can give them rewards like allowing access to some articles, downloads etc. the purpose of all these features is to increase user engagement on your site so that you can get more page views, high business ranking and more clicks on affiliate and other earning programs.