Firefox Developer Tools - Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile.
LiveReload - LiveReload 2 proudly presents… The Web Developer Wonderland. (a happy land where browsers don't need a Refresh button). CSS edits and image changes apply live. CoffeeScript, SASS, LESS and others just work.
Google Chrome Developer Tools - Get started with Google Chrome's built-in web developer tools.
Browsersync - Browsersync makes your tweaking and testing faster by synchronising file changes and interactions...
TrueMetrics Analytics Inspector - Analytics Inspector provides an easy way to validate web analytics and marketing integration, as well as offers a great way to quickly validate the instrumentation via the unique and simplified user interface.
CodeKit - CodeKit allows you to optimize the performance of your website by automatically and efficiently compiling a variety of popular languages.