CSS Lint points out problems with your CSS code. It does basic syntax checking as well as applying a set of rules to the code that look for problematic patterns or signs of inefficiency. The rules are all pluggable, so you can easily write your own or omit ones you don't want.
Your favorite site doesn't provide news feeds?
This free online service converts any web page to an RSS feed on the fly.
To help you find the perfect CSS-reset styles, CSSresetr lets you try all the best CSS Resets on a variety of web pages – even your own.
A fun and easy way to share ideas on a website
Page2RSS is a service that helps you monitor web sites that do not publish feeds. It will check any web page for updates and deliver them to your favorite RSS reader.
Advanced CSS Prettifier
Take snapshots of any Web page
Procedural drawing tool
Beautify, unpack or deobfuscate JavaScript and HTML, make JSON/JSONP readable, etc.
Mockingbird is an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application.
YOURLS stands for Your Own URL Shortener. It is a small set of PHP scripts that will allow you to run your own URL shortening service (a la TinyURL or bitly).
PunyPNG is a free website optimization tool that dramatically reduces the file size of your images without any loss of quality.
(X)HTML5 Validator
Landing page optimization for your mocks and wireframes.
Fivesecondtest helps you fine tune your landing pages and calls
to action by analyzing the most prominent elements of your design.
Digital Publishing Platform
Color palette generation tool