KnownOutage - Quickly and easily alert people when there is an issue or outage with your service.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Cachet - Cachet is a free, open source status page for your API, service or company. Built with all of the features that you'd expect from a status page.
RPi-Monitor - RPi-Monitor is a tool that provides all the connected system peripherals properties and current metrics.
Stashboard - Stashboard is a status dashboard for APIs and software services.
MenuBar Statistics - MenuBar Statistics is a lightweight app that sits quietly in your menu bar of macOS and displays computer information such as CPU, Disk, and Network, which is updated every 5 seconds.