The CWE/SANS Top 25 Most Dangerous Software Errors is a list of the most widespread and critical errors that can lead to serious vulnerabilities in software. They are often easy to find, and easy to exploit. They are dangerous because they will frequently allow attackers to completely take over the software, steal data, or prevent the software from working at all.

Eloquent JavaScript is a book providing an introduction to the JavaScript programming language and programming in general.

Retrospectiva is an open source, web-based, project management and bug-tracking tool.
It is intended to assist the collaborative aspect of work carried out by software
development teams through the use of blogs, a wiki and tickets.

Ajax GUI Framework

A sexy server logger console in Firebug

The flexible, fast, and secure template language for PHP

Online Regular Expression Testing Tool

a PHP Template Engine

Google App Engine lets you run web applications on Google's infrastructure. App Engine applications are easy to build, easy to maintain, and easy to scale as your traffic and data storage needs grow. With App Engine, there are no servers to maintain: You just upload your application, and it's ready to serve your users.

JS Bin is a tool for experimenting with web languages. In particular HTML, CSS and JavaScript, but JS Bin also supports other languages too (like Markdown, Jade and Sass).
JS Bin is ultimately a code sharing site.

Pipes is a powerful composition tool to aggregate, manipulate, and mashup content from around the web.

Web Based Ajax Development Tool

The native Windows binding for PHP

Stack Overflow is a question and answer site for professional and enthusiast programmers.