There are many free web APIs out there now that you can integrate your mobile app, web app, or website with to easily add some very powerful features. A web API is an application programming interface which can be accessed over the internet using web-specific protocols.

Some big names/companies expose their features/data for you to freely use in your own apps/websites this way. Here are 9 that I think could be used to make some great projects:

1. Spotify API (music)

With the Spotify API, you can integrate your app/website to discover music, play a user’s music, create playlist for a user, and more. For example, you could create your own music playlist discoverer and builder based on a user’s interests.
Spotify developer website

2. Wit.ai API (text/voice processing)

With the Wit.ai API, you can process text or speech and turn it into recognizable actions that your app/website can use. You could use this to build an intelligent bot for your app/website.
Wit.ai website

3. Plaid API (bank account connect)

With the Plaid API, you can allow user to connect their bank account without you knowing the details. The Venmo app already uses this! It’s only free for testing and then paid.
Plaid API website

4. Social Media APIs (Facebook/Insta/etc.)

With these various APIs, you could allow login through a user’s social media account, post on behalf of a user, and retrieve a user’s profile. Plenty of app/services already use these as you know.
Facebook Developers website

5. Genius API (lyrics)

With the Genius API, your app/website can look us song lyrics and the meanings for the lyrics. For example, you could create a Tupac lyric-spitting bot.
Genius Developers website

6. BetterDoctor API (healthcare provider)

With the BetterDoctor API, you can integrate your app/website with nearby health provider information. For example, you could look up a user’s nearest dentist based on their insurance and location.
BetterDoctor developer website

7. Recipe Puppy API (recipes)

With the Recipe Puppy API, your app/website can look up recipes based on ingredients and search terms. For example, you could make and app that randomly gives a recipe each day based on what’s in the user’s fridge.
Recipe Puppy API website

8. eBay API (shopping/selling)

With the eBay API, your app/website can automatically search, buy, and/or sell on eBay. For example, you could make a website/service that automatically lists a user’s item for sale based on the best time of day.
eBay developer website

9. Bible API

With the Bible API, your app/website can access Bible books, chapters, verses, etc. For example, you could make an app that automatically provides a Bible verse based on the day’s world news.
Bible API website

There are so many more that I didn’t list and let me know if you know of some more good ones. Also, let me know what types of projects could be done with some of these.