This is a very uniformly and carefully formatted, RESTful joke API. It doesn't need any API token, registration or payment and CORS has been enabled. The payload is served as JSON, XML or YAML.
Most APIs didn't have uniformly formatted jokes or additional filtering methods (to for example filter out NSFW jokes). The JokeAPI has those features plus the standard features other joke APIs have.
JokeAPI recently had a major overhaul which completely changed the syntax. For more information, please read the documentation.