How Slack used message buttons to simplify a common workflow
When a helpdesk ticket is created in a 3rd party system, send an actionable notification in Slack that allows the user to claim the ticket or apply a label.
Allow team members to quickly set up their own incoming webhooks without needing to create a Slack app.
Create a watchdog bot that enforces your team's draconian hold on channel nomenclature.
Automatically send a direct message to new team members asking them to accept a terms of service or code of conduct.
Allow people to post announcements to a restricted channel from time to time, with admin approval.