"To ensure the best possible product experience for SolarWinds® Pingdom® users, and to focus our resources and investment on this next phase of our product development, we will no longer offer our free plans as of February 6, 2019.
To continue enjoying the benefits of Pingdom, all free users will need to sign up for a paid subscription plan option by this date."
For someone who just wants to know if a site is up or down, and has a dozen cheap or free services to choose from (I also sometimes use UptimeRobot), it's not a market Pingdom really caters to anymore.
Anyways, this is also the reason I built Server Check.in[1] a few years back[2]; mostly for my use, and it's been a fun ride! Building a distributed, microservice-ish thing over the course of 7 years has been interesting. Would love to answer questions about it if you have any.
[1] https://servercheck.in/ [2] https://news.ycombinator.com/item?id=4901350
Disclaimer: I'm a maker of Freshping (https://www.freshworks.com/website-monitoring/)