You can leave a reputation for posts and threads that catch your attention, for good or bad. The reputation points can be positive and / or negative. You can also leave a comment as well to go with your reputation point (s).
Reputations can also be left anonymously. This is group permissioned based. Only users with permissions to view anonymous reputations will be able to view the anonymous reputations. Users receiving anonymous reputations will receive an alert informing them of that fact. You can also prevent a specific group from giving a negative reputation.