This is one of the best known and used public APIs. It serves almost two billion requests per month, an outrage!
This API offers you typical application data, such as users, tasks, photos, posts, comments, albums, etc. These are various data sources that you can consume with your endpoints in the perfectly standard REST API style.
Even the data that is offered is related, for example, the comments belong to the posts or the albums have photos.
We can use this REST API without any registration.