It's free if you don't have too many servers - 15 uptime monitors (the most useful) and 32 blacklist monitors (useful for e-mail, but don't know why you'd need so many compared to uptime).
It's fairly easy to reach the free limits with not many servers if you're also monitoring VMs, but I've found it reliable so far. It's nice you can have ping tests from different locations, and it collects pretty much any metrics that are useful such as CPU, RAM, network, disk. The HTTP and SMTP tests are good too.
It's free if you don't have too many servers - 15 uptime monitors (the most useful) and 32 blacklist monitors (useful for e-mail, but don't know why you'd need so many compared to uptime).
It's fairly easy to reach the free limits with not many servers if you're also monitoring VMs, but I've found it reliable so far. It's nice you can have ping tests from different locations, and it collects pretty much any metrics that are useful such as CPU, RAM, network, disk. The HTTP and SMTP tests are good too.