OneKontest

OneKontest helps you to engage & reward your followers through Twitter contests. #Hashtag Contests: Tweet a Twitter #hashtag to enter. You may also require users to follow your account. Photo Contests: Tweet or upload a photo to enter. Services supported: Instagram, Twitter, TwitPic, Yfrog. Video Contests: Tweet a video to enter. Services supported: Vine, Instagram, YouTube, Vimeo. Trivia Contests: Answer a trivia question to enter. Winners are selected from the users who answer it correctly. Feedback Contests: Answer a question to enter. Reward your users for their feedback.

Screenshots from Chrome Web Store