Slackbox - Spotify playlist collaboration through Slack
RightGIF - Less noise, better GIFs. A better /giphy for Slack.
VixT on Slack - The best video mashup app now on Slack.
Remixatron - Infinite Jukebox on the command line in Python.
Slack Meme Bot - Spice up your team conversations with memes
GoGifApp - Free Slack GIFs App, multiple images to pick from at once