To begin, Firefox and Chrome, of course, are the browsers of choice for a web developer.
Tools for Firefox
Firefox has tons of tools for web developers! Take special note of:
- DOM Inspector,
- HTML Validator,
- SQLite Manager,
- Web Developer.
If using Firebug, then also take special note of Acebug, FireRainbow.
Tools for Chrome
Chrome is younger and has less tools, but many web developers prefer Chrome over Firefox. And there are definitely tools:
- Google Chrome Developer Tools
- Web Developer
- Firebug Lite
Color Generator Eye Dropper
dust.js has been selected by LinkedIn recently as their templating engine to unify the way web pages designed in HTML and CSS gets filled with data generated by other server based programs written in various languages including Java, Grails, and JRuby. It is free and open source (looks like MIT license)
PhoneGap is a free and open source (Apache License) library for writing cross-mobile-platform HTML5 app to access technologies native to the mobile platform (vs. programs being stuck in the browser).
For building gesture/touch-enabled UI for cross-mobile-platform Apps, there is jQuery Mobile, which is a very young project still, and is free and open source: dual licensed under MIT and GPL2. There is also Sencha Touch, a more mature library that is free and open source, cross-licensed under GPL3, a modified GPL3, a free (as in beer) commercial software license, and a paid commercial OEM license.
You might also need a library to add MVC or MVVM structure to your App. For that, consider Backbone.js (MVC) or Knockout.js (MVVM).
For everything else, there's jQuery.