Peer-to-peer data in the web browser.
PeerJS completes WebRTC as an API abstraction, connection broker, and binary serialization format

Nice write-up on techniques for scaling up a web application.

Codebender is an embedded development platform with an emphasis on the Arduino and it’s completely web-based, so you don’t have to install, manage and update anything.

MySQLTuner is a script written in Perl that will assist you with your MySQL configuration and make recommendations for increased performance and stability.

dbv.php is a database version control web application featuring schema management, revision scripts, and more!

Code review tool for Git projects.

Instant coding answers via the command line.

Baïkal offers ubiquitous and synchronized access to your calendars and address books over CalDAV and CardDAV. Baïkal implements the current IETF recommendation drafts of these industry standards for centralized calendar and address book collections.

Hurl.it makes HTTP requests.

Choose the request method, customize headers and POST parameters, add basic authorization or OAuth credentials, and even follow redirects. Then view the nicely formatted request and response.

It's the perfect tool for testing APIs. Just enter a URL and click send.

Testing an HTTP Library can become difficult sometimes. PostBin.org is fantastic for testing POST requests, but not much else. This exists to cover all kinds of HTTP scenarios. Additional endpoints are being considered (e.g. /deflate). All endpoint responses are JSON-encoded.

HTML5 Webcam for your website

Popcorn Maker makes it easy to enhance, remix and share web video. Use your web browser to combine video and audio with content from the rest of the web — from text, links and maps to pictures and live feeds.

Selfspy is a daemon for Unix/X11 and (thanks to @ljos!) Mac OS X, that continuously monitors and stores what you are doing on your computer. This way, you can get all sorts of nifty statistics and reminders on what you have been up to. It is inspired by the Quantified Self-movement and Stephen Wolfram's personal key logging.

Python SQL injection framework

WebScarab is a framework for analysing applications that communicate using the HTTP and HTTPS protocols.

Your unofficial guide to dotfiles on GitHub.

Flask is a microframework for Python based on Werkzeug, Jinja 2 and good intentions. And before you ask: It's BSD licensed!

Cross-Origin Resource Sharing (CORS) is a specification that enables truly open access across domain-boundaries. If you serve public content, please consider using CORS to open it up for universal JavaScript/browser access.

Vega is an open source platform to test the security of web applications. Vega can help you find and validate SQL Injections, Cross-Site Scripting (XSS), inadvertently disclosed sensitive information, and other vulnerabilities. It is written in Java, GUI based, and runs on Linux, OS X, and Windows.

VeeWee: the tool to easily build vagrant base boxes or kvm,virtualbox and fusion images