rapidapi.com - vast selection of APIs from different vendors. Many are broken or not great, so you'll have to sift through to find the good ones.
linkpreview.net - get the title, description, thumbnail, icon, etc of any website
abstractapi.com - many useful APIs for web developers. Geolocation API is great!
getping.info - Trigger an email or slack notification with a simple GET request
linkpreview.net - Get info about a website with a quick and simple GET request
NoCodeAPI.com - use various apis without having to sign up with each vender