Today Freek from spatie released a new package:
Laravel-uptime-monitor is 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 5.3’s notifications, so it’s easy to use Slack, Telegram or your preferred notification provider.
UPDATE 2016.01.03: A standalone version (read: version that doesn’t require Laravel knowledge) has also been released:
Under the hood the uptime-monitor is a vanilla Laravel 5.3 application with the laravel-uptime-monitor installed into it.
Laravel Uptime Monitor →
An uptime and ssl certificate monitor written in PHP →