intoDNS is described as 'checks the health and configuration of DNS and mail servers' and is an website in the Network & Admin category. There are more than 25 alternatives to intoDNS, not only websites but also apps for a variety of platforms, including SaaS, Windows, Linux and Mac. The best alternative is Pingdom. It's not free, so if you're looking for a free alternative, you could try MxToolBox or Curler by Amixr.IO. Other great sites and apps similar to intoDNS are Up Ninja (Paid), Silent Down (Paid), Netthrob (Paid) and RapidSpike (Paid).
* Uptime monitoring - checks are performed approximately once every minute from one of the available locations worldwide. During downtimes, checks are performed from four different locations simultaneously. Downtime is only recorded if more than half of servers can confirm it.