Data USA
Data USA lets users use population data from the United States for free for your own use as long as credit is given to Data USA. All requests for commercial use need to be run by Data USA.
PlaceKitten
PlaceKitten lets users retrieve photos of kittens for use as placeholders in a design or some code. All the photos are free to use, but a note with credit to the photographer is encouraged.
Animechan
Animechan lets users retrieve random anime quotes by title or character and can either be a single quote or 10 random quotes at once! All of the quotes are free to use.
Summary
There are a lot of free public APIs out on the internet! They range from random photos of dogs, cats, pixel designs of monsters, US data population data, times that the sun sets and rises, and so many more. My favorite one I have found so far is Animechan with all the random anime quotes.