For years I had OpenACS’s Uptime (dead link) monitoring my main web server. I hadn’t thought about it for a while, but while reviewing logs I noticed there are no queries to /uptime.txt, and my last email from them was in October 2013 as was the last logged uptime.txt request.
Greenspun’s site suggests the site is read-only or unmaintained.
Oh well, I was intenting to get AWS Lambda to monitory my sites, anyway. Got a lot of use out of Greenspun’s free service, so no complaints.