For the last few weeks Iv been working on a new website in my spare time. Its now live and is at runslikeclockwork.com. Its a server monitoring tool where you add your sites and you will get an SMS alert when a site goes down / comes back up again.
Its slightly different from most other services because it checks the rendered HTML of a page for a keyword or phrase specific to that site. This covers you when you misconfigure an Apache/Nginx Virtualhost which can sometimes leave you with the wrong site being served on a domain, but of course the server is still giving out 200 status headers.
At the moment its very simple but I am planning on adding some more features over the next few weeks.