GitHub + Slack Integration - Full visibility into your GitHub projects right inside Slack
Clearbit for Slack - Send all signups directly to a Slack channel
Stack Overflow Documentation - A crowdsourced developer documentation
Photostash - Automatically save your pictures from Slack to Gdrive
ask-stack - Get answers from Stack Overflow directly in the Atom editor
Slack It - A bookmarklet to share links in Slack with one click