I have developed several custom APIs using PHP Yii framework.
most Popular API's I have worked on are shown below:-
=> Google Maps
=> Twitter
=> YouTube
=> Flickr
=> Amazon
=> Twillo
=> Facebook
=> eBay
=>[login to view URL]
=> Google
=> Search
I use the following web protocols and web API format:-
REST, SOAP, JavaScript, XML-RPC
XML, JSON, RSS, HTML, PHP, Text, CSV
Google Map/XML/JASON API: [login to view URL]
Facebook/Twitter API: [login to view URL]
REST/JASON/XML: [login to view URL]