Free open source alternative to pingdom? [closed]

I'm not familiar with Pingdom, but I think Smokeping will do everything you want. If you specifically want to monitor an HTTP/HTTPS server and not just general connectivity (by way of ICMP), check out the EchoPingHttp and EchoPingHttps probes. There are also probes that will monitor DNS and SSH services.

We use smokeping for general latency and "network health" monitoring all over our network with good results. I just used it last week to help diagnose a duplex mismatch at a remote site.

Setup is pretty minimal, especially if you are familiar with Linux.

Why don't you do it on your own rather than using services like pingdom or alertfox?