Words API
The Words API is “an API for the English Language” that has a wide array of functions such as extracting word definitions or synonyms, retrieving word or phrase example usage, getting rhyming words, and much more.
https://www.wordsapi.com/#try

Skyscanner Flight Search API
The Sky Scanner API lets you search for flight & get flight prices from Skyscanners database of prices, as well as get live quotes directly from ticketing agencies.
https://rapidapi.com/skyscanner/api/skyscanner-flight-search

TrueFace API
TrueFace.AI is an advanced facial recognition API that can identify faces, emotions, gender, age and more. TrueFace.ai can even differentiate between a face and a picture of a face – a common flaw of some other facial recognition APIs.
https://trueface.ai

HTML Drag and Drop
Users select draggable elements with a mouse, drag the elements to a droppable element, and drop those elements by releasing the mouse button. The dropEffect can be defined as copy, move, or link. ;

Merriam-Webster Dictionary
The Merriam-Webster Dictionary API gives developers access to a comprehensive resource of dictionary and thesaurus content. Make your applications better by integrating our authoritative definitions, etymologies, audio pronunciations, synonyms and antonyms, and more.

International Space Station Current Location
This is a simple api to return the current location of the ISS. It returns the current latitude and longitude of the space station with a unix timestamp for the time the location was valid. This API takes no inputs.
http://open-notify.org/Open-Notify-API/ISS-Location-Now/
Ambient Light sensor
The ambient light events are a handy way to make a web page or an application aware of any change in the light intensity. It allows them to react to such a change, for example by changing the color contrast of the User Interface (UI) or by changing the exposure necessary to take a picture.
https://developer.mozilla.org/en-US/docs/Web/API/Ambient_Light_Events

1 - Youtube - Includes different tools for sorting videos into lists, such as listing by keyword, location, live, etc.
2 - Google Calendar - You can create and edit Google Calendar events. This is how we can email Google Calendar invites through Gmail, integrate with Google Maps, etc.

The NASA API makes NASA data and imagery accessible to application developers. Jservice is a trivia API

These are News API's that can be used on websites that involve news that updates.

1. Pocket.com API: "save-for-later" feature can be integrated into native apps and websites. Pulls data from websites (web scraping) // 2. Pinterest API: allows users to access Pinterest data for more interaction. Can add a Pinterest button to "Save, follow, pin, etc." to increase engagement. // 3. Twitter Direct Message API: enable developers to build better-personalized customer experiences at scale as well as other innovative interactions

FullContact provides information about the person behind an email address: full name, age, location, gender and social network accounts.
Okta -- formerly Stormpath is a secure user management API with built-in support for Facebook login (and a few others).

#1 - Google Analytics for embedding analytics dashboard into 3rd party sites, #2 - Google Calendar API for creating, managing, and displaying events,
#3 - Historical, real-time and nowcast weather data

On the Twitter developer page, you can use their code for several different APIs, like ads and engagement. For the engagement one, it helps you see all of the activity on a tweet as far back as 90 days.

The Ist API was to create a cross-brower video player; the 2nd API was to get access to users' media ; the 3rd API was to animate a video.

The first is a useful API by Google that provides very clean looking charts. You can import and display data easily with it.

The second API allows for the integration of the Spotify library to your website.

The third API takes all the Pokemon data and provides a REST API for accessing it.