Check if your servers are up by pinging them. Ping uses the ICMP protocol and records how long it takes a packet to reach a particular host and be sent back. If that packet is never received, then this can indicate that the server or some part of the network is down. Think of it as an early warning!
Various statistics are collected:
Total pings received
Latency standard deviation
Alarm if a host stops replying to pings
Color coded status of hosts so it's easy to see at a glance which hosts are up and which are down
Can use IPv4 or IPv6 - a great way to check if your network and servers are working in IPv6
A slick UI - swipe to enable/disable, re-ordering of hosts, tapping a host shows/hides extended info, etc
You can also use ping to check if your internet is working. Try pinging your ISP or a well known host.