Premise: Recruiters spam left and right, so we decided to create a website just so they could get a familiar calendar-like interface but asked them to pay for your time. As soon as we exposed the external version with the URL, we decided to make an automated template ("Great. Please book a slot on my calendar and we can chat more about this. You'll receive my resume upon confirmation of the booking. https://bk.poachme.dev/Lazaro"). After that we ended up creating a virtual business card service so that could easily create a web presence without going through a different service (https://bk.poachme.dev/kBMf).
Availability: Web
Price: $0
Cost: Nearly nothing, it just sits with my other hosted services.
Why do it? Honestly, asking someone to pay for your time is the easiest way to see who values your time. The cost to send a single spam message to thousands of developers is nearly zero and it takes time to sort through the messages to see if there's anything good. I have had experiences going from blackmail all the way to people disclosing the actual salary for the position without any money exchanging hands which proves that when your time has value it's suddenly possible for the pay bracket for a position to appear.