Slackin - Create your own public Slack chat community
Slofile - A public Slack database with live channel & member stats
Message Bender - Backup and delete all Slack messages in bulk
2000 (!) Slack Groups - The largest curated list of verified Slack groups
Slack Archive - Public, searchable & browseable archive of Slack channels
Hamster Pad - A social network built on top of Slack