Talkus - Chat with your website users from Slack
Message Bender - Backup and delete all Slack messages in bulk
Chatlio - When you have a business to run, your average instant messaging software just will not do. You need an internal presence upon which your entire team can collaborate on. Read more about Chatlio.
Slack Deletron - Delete files from your Slack Workspace!
Slacking Pigeons - Chat in real time with your users directly from Slack
Public - Group chats.