Apiary – Service for API mockup and testing
http://apiary.io/
JSON Editor
https://www.jsoneditoronline.org/
JSON Validator
http://jsonlint.com/
CSS3 Generator
http://css3generator.com/
CSS3 Playground
http://css3.mikeplate.com/
CSS3 Button generator
http://css3button.net/
Ultimate CSS gradient generator
http://www.colorzilla.com/gradient-editor/
CSS 3.0 Maker
http://css3maker.com/
FavIcon Generator
http://tools.dynamicdrive.com/favicon/