This API allows you to see US public data such as the population of a state, the salaries of different jobs, price of certain colleges with acceptance rates, and more. Data USA is free for anyone to use and it allows its users to help see the current social and economic trends currently in the U.S. and any other information you may need. This is overall an API best for anyone looking for a job, college, degree, and more, but it can also be used to learn fun facts about the U.S. from population and other U.S. public data.
IMDB is a public API that allows you to see ratings for movies and tv shows while also being a great website for all things movie/show related. This includes cast members, theater ticket prices/showtimes, trailers, and more. This API is free and you can do other things like add movies/shows to your watch list and leave a review/rating on something you just watched. IMDB is an API that updates real-time while also being a graphQL-based API which is better for a website like this. Overall, IMDB is a great free API for anyone looking to see pretty much anything related to movies and shows while also being easy to use and understand.
Imgur is another free API that allows you to interact with the websites infrastructure through programming. This website is meant for post pictures and videos for other's to see. The most common things you will come across on Imgur is memes as it is known to be one of the most popular sites for posting memes and funny pictures. Imgur is known as a RESTful API meaning two computers can exchange information over the internet efficently and safely. This is overall a great API that allows you to mess with code through HTTP requests and JSON responses.
In the end, all of these are great websites with great APIs and each one is very different. Each of these APIs work differently and the user can interact with them differently depending on what type of API it is.