Mist.io is described as 'Mist is an open source multicloud management platform. It supports all popular infrastructure technologies including public clouds, private clouds, hypervisors, containers and bare metal servers'. There are more than 25 alternatives to Mist.io for a variety of platforms, including Online / Web-based, SaaS, Windows, Linux and Mac. The best alternative is Pingdom. It's not free, so if you're looking for a free alternative, you could try Spiceworks or Freshping. Other great apps like Mist.io are Cabot (Free, Open Source), New Relic (Freemium), isUp (Free) and Nodeping (Paid).
Pingdom web site monitoring and other infrastructure for you and instantly let you know when anything goes wrong. Measure uptime, downtime, and the performance of your website as experienced by visitors.
Website/Server monitoring with fast notification via Web, SLACK or E-Mail on issues. What you get: 25 monitors, checked every 15 minutes. Now includes SSL-Certificate validation and port checks. Totally free!.
Pingbreak is an original and free monitoring service. Get notified through Twitter if your website is down.
Pingbreak checks all of your websites each minute and alert you instantly by Direct Message (DM).