Online and Offline is described as 'The most frustrating part for the website owner is the failure of the internet connection with their site. If you find that you cannot access your website. Do not be panic. Most website owners feel that there is some kind of problem in the backend/server's end'. There are more than 50 alternatives to Online and Offline for a variety of platforms, including Online / Web-based, SaaS, Android, iPhone and Mac. The best alternative is Pingdom. It's not free, so if you're looking for a free alternative, you could try Down For Everyone Or Just Me? or Freshping. Other great apps like Online and Offline are Cabot (Free, Open Source), isUp (Free), HetrixTools (Freemium) and Is It Down Right Now? (Free).
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 5 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).
Monitor uptime,response timeandapdex indexes of your website or api for free and receive instant updates through e-mail or Slack with real time announcements. Don't leave your customers in the dark during downtime & outages of your website.