Slackin - Create your own public Slack chat community
Hamster Pad - A social network built on top of Slack
Message Bender - Backup and delete all Slack messages in bulk
Doof - Share your hopes and dreams.
sup3rS3cretMes5age - A safe, simple tool for one-time (self-destructing) messages
Slack Archive - Public, searchable & browseable archive of Slack channels