Apigee - Intelligent and complete API platform
API Connector by Mixed Analytics - Connect any API to Google Sheets.
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing
SheetHub - SheetHub turns your spreadsheets (either Google Sheets or Excel Online) into a REST-ful JSON API.
Postman - The Collaboration Platform for API Development
Hoss - Track and manage third-party APIs