StatusOk (Open source) - Get notified through Slack/email when your website is down
Haark - Tracks your sites and notifies you if they're down
Troops Slack Sales Gong - The most customizable Salesforce Gong in Slack
Rollie - Know where your money goes. Spending tracker for iPhone.
UXPin + Slack - Keep tabs on design projects in Slack
CostTeam - Identify online subscriptions and other recurring expenses.