Free Ping Tool is an easy-to-use utility which allows you to monitor the availability of local network devices and remote websites.
Enter the host name or address of whatever resource you'd like to check, click Add, then Start, and the program will use ICMP Ping to check for its presence. Pings will be regularly repeated, and the results displayed on a table and a graph. And the program can check up to 10 devices or websites at the same time.
If your target resource blocks pings - the PC has a firewall, for instance, or your website's server isn't configured to return them - then Free Ping Tool won't tell you anything useful.
If the resource does return pings, though, Free Ping Tool will allow you to see its availability at a glance (just check the Status column on the Ping Data graph: green means online, red means offline). And the Ping Graph will show you how this availability has changed over time.
As a bonus, Free Ping Tool also includes a free graphical TraceRoute option. Just click the Trace Details tab, enter your host name or IP address in the box, and click Trace. In a moment you'll see a neat chart showing every system between yourself and the target, along with its Round Trip Time (RTT).