1. Autoprefix

Usage: Auto add vendor prefix for your css code.
Link: https://autoprefixer.github.io/

2. CSS Matic

Usage: A site with tools help you to generate Gradient, Box shadow, Border radius code.
Link: https://www.cssmatic.com/

3. CSS Shapes

Usage: Create shapes with a single HTML element.
Link: https://css-tricks.com/examples/ShapesOfCSS/

4. Font converter

Usage: Convert font
Link: https://transfonter.org/

5. Optimize image

Usage: Compress image
Link: https://tinypng.com/

6. Text shadow Generator

Link: http://owumaro.github.io/text-stroke-generator/

7. CSS Filter Generator

Link: http://bennettfeely.com/filters/
Link (manual): http://www.cssfiltergenerator.com

8. Stripes Generator

Link: http://stripesgenerator.com/

9. CSS Pattern Generator

Link: http://www.patternify.com/

1. ColorZilla

Usage: Pick color code directly from browser
Link: colorzilla

2. CSSViewer

Usage: View CSS code while hovering
Link: cssviewer

3. Page Ruler

Link: page-ruler

1. Mastering the :nth-child

Link: http://nthmaster.com/