Lurchr - Saves all your Slack links, so you can focus on work
Whatis - Manage & organize your team's knowledge straight from Slack
Tettra - Tettra is a company wiki that helps teams manage and share organizational knowledge.
Slack-News - Read news from multiple sources within Slack by just typing
Slack It - A bookmarklet to share links in Slack with one click
Photostash - Automatically save your pictures from Slack to Gdrive