This website is running on a Linux virtual machine hosted in Oracle's Cloud for free. Oracle offer an Always Free tier of service that generously allows you to run two virtual machine instances for free. [Feb 2022 update - plus up to four ARM-based instances]. Running a single virtual machine of a comparable size in Digital Ocean's cloud costs about $50 a year, so it's a generous deal.
Oracle's sign-up process requires a credit card to prove you are a real person, but I've had several years of service and paid absolutely nothing so far. One downside is that the instances are part of a larger cloud offering, and configuring everything is more complex than simpler offerings from competitors. Specifically, things like networking need to be configured at the cloud layer, e.g., to allow incoming HTTP traffic to your VM instance.
If you are interested in running your own instances, see the Always Free Tier information on Oracle's website. Note that this is distinct from the similarly named Free Tier, which provides limited free credits for a wider range of services for a limited time, after which you pay.