If you want to start looking for APIs to use in your projects, I recommend you begin with these fantastic resources

• Todd Motto’s list of public JSON APIs for use in web development is a perfect start
• Abhishek Banthia’s Public APIs has an equally extensive list of APIs from round the web.
• http://apis.io - an experimental API Search service to help discover APIs on the web.
• https://market.mashape.com/explore - has a searchable categorized list of APIs on the web
• You can also search ruby gems to find out if there’s a gem/library for ruby that makes it easy to interact with an API too.