http://css.spritegen.com/

http://css.spritegen.com/- Optimize your website using CSS Sprites! Generate CSS Sprites to speed up your website by reducing HTTP requests.

http://regexr.com

RegExr is an online tool to learn, build, & testRegular Expressions (RegEx / RegExp).

https://robots.thoughtbot.com/transitions-and-transforms

https://robots.thoughtbot.com/transitions-and-transforms