Is It Down Right Now? - Network & Admin
StatusOk (Open source) - Get notified through Slack/email when your website is down
Is it Down? - Is it down can check if a website is down or is it just your PC that can not access it.
Better Uptime - We call you when your website goes down
Site Down - Site down outage and downtime reports from SiteDown.co
Is it down by Freshping - Check if any website is down from 5 global locations