Laravel-uptime-monitor is a laravel package that provides a powerful, easy to configure uptime monitor. It will notify you when your site is down (and when it comes back up). You can also be notified a few days before an SSL certificate on one of your sites expires. Under the hood, the package leverages Laravel native notifications, so it’s easy to use Slack, Telegram or your preferred notification provider.
If you’ not familiar with Laravel, but still want to use this uptime monitor, take a look at the uptime-monitor-app repo which contains a stand alone version of this package.