Tagsdock - Tag Instagram photos instantly from your iOS keyboard.
Watch2Gether - Watch2Gether is an app that allows multiple people to watch the same content simultaneously and interact with each other while watching.
RiteTag - No idea which hashtags to use? Get instant hashtag suggestions for images and texts on desktop and mobile.
Metastream - Watch streaming media with friends
Hashtag Suggestions for Instagram - Find the best hashtags for every photo
StreamParty - StreamParty is a watch communiry, that allows you to watch video streams in sync with the people you care about, on multiple services.