Piotr Zalewa has created a really great playground, jsFiddle, for testing sample code and playing with the Web. With an area for the holy trinity of the Web (HTML, CSS, JS) and an output region, you can get right to hacking.
It goes beyond this though. You can also add resources, an Ajax echo backend, and [...]
Normally we use CSS selectors to find and tear apart HTML. Sergey Chikuyonok’s jujitsu move is to do the opposite. With Zen Coding you take a CSS selector like this:
PLAIN TEXT
HTML:
html:xt>div#header>div#logo+ul#nav>li.item-$*5>a
and it generates an HTML structure like this:
PLAIN TEXT
HTML:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en”>
<head>
<title></title>
[...]
Joseph Pecoraro has made some major improvements to Web Inspector.
It is now much easier to create and much around with the content. Create new CSS selectors with ease; Add content in-line with elements; see color representations of any value.
And, there is more:
DOM Storage
The DOM Storage DataGrids now displays live updates. You don’t need to manually [...]
Our very own Ben Galbraith took a dip down under to talk about the state of developer tools.
The session description is:
For many years, developing for the web left quite a bit to be desired when it came to the tools at developers disposal, particularly in comparison with the sorts of development environments available for desktop [...]
Aaron Conran has published a new preview of Ext JS Designer which includes the new features:
Duplicating Components
Transforming Components
Undo/Redo
Configuration Searching
Auto Updating
Screenshots
It is a great time for new tools popping out with Atlas coming along nicely too…. and a couple more being hacked on. Open Web Tools FTW! 
Our Webmonkey friends have featured Opacity, a vector image manipulation tool that has a couple of features that are interesting for Web developers wanting to do HTML5-y things:
To use the new source code feature in Opacity, simply design your vector-based graphic or animation sequence and, once you’re happy with it, head to the Inspector menu [...]
FireCrystal is a Firefox extension that helps designers and programmers alike figure out how interactive behaviors on the web work. FireCrystal allows users to record and rewind their interactions with web pages while showing the relevant code.
Conrad Chu, Design Director at Ask.com, thought he needed an image compression tool better suited for designers and front-end developers (compared to smush.it) and scratched the itch with pungpng.
punypng is serious about image compression — it handles 8-bit PNGs, 24-bit PNGs, JPEGs, GIFs and animated GIFs. It also leverages dirty transparency techniques to further [...]
Kangax stumbled upon a blog post by Remy Sharp on detecting global variable leaks. He took that work and updated it a little to filter out Prototype, Script.aculo.us, Google and Mozilla globals.
If you want to add sets it is easy to do so… go fork away. The bookmarklet itself is here.
Of course:
It’s worth mentioning that [...]
Chris Vanrensburg has created a curve explorer that gives you a nice visualization of curve functions which are used for animations (easing and the like).
Chris has more:
I looked at the work of Robert Penner, since it seems to have become the gold standard for motion curves. Nice stuff, and it inspired me. I wanted to [...]