Jo is an open source mobile application framework that is based on HTML5 .
It enables you to create for multiple platforms like webOS, iOS, Android, Symbian, Safari, Chrome and Dashboard Widgets.
The framework is small in size, ~8kb, without any dependencies and compatible with many other JS frameworks.
Jo is also compatible with PhoneGap and makes possible to create native apps besides web apps.
It is very well-documented and has sample codes on every level.
Requirements: No Requirements
elRTE is an open source and feature-rich WYSIWYG editor that is built using jQuery UI.
It performs all standard functions of an editor and has all the extras like undo-redo, advanced table management, creating a custom HTML element with a custom style + inserting it quickly and more.
The interface is controlled via a single CSS file and can be customized pretty easily.
It has a built-in "save" button which can be attached to a JS function that saves the content that is pretty useful for helping users not to lose their content.
elRTE can be integrated with any file manager, however, there is elFinder, a file manager that has ready-to-use integration (can be used standalone too).
Requirements: jQuery, jQuery UI
Compatibility: All Major Browsers
Similar to the popular disposible chat websites (check 7 Free Disposable Chat Systems For Instant Communication), Anologue is an impressive one which is open source.
It works by simply clicking on a "new room" link and the application instantly creates a chat room with a unique URL where you can invite others.
The application is totally Ajaxed, built with PHP and uses the Lithium Framework, CouchDB and jQuery.
And, if you don't prefer to install your own, you can still use Anologue as the hosted version is free for everyone.
Requirements: PHP 5.3+, CouchDB, rad-dev account
Nuggetz is a free CMS application for easily and quickly controlling websites where the content is not stored in a database.
It is powered with PHP and integrates with any website design. You can simply make a section of a web page editable by calling a code like
$mynugget = new nuggetz("name");.
The application works with modal boxes and, once logged in, the editable sections are displayed like the screenshot above.
You can click to any section and edit it inside a WYSIWYG editor. The content is saved inside the files themselves (just like an HTML file).
Compatibility: All Major Browsers (except IE6)
Show Slow is an open source tool (and, optionally, a free web-based service) for monitoring website performance metrics over time.
It simply collects the results from YSlow and Page Speed rankings and graphs them to show you how various changes to the website can affect the performance.
And, it can do this regularly to help you see the improvements done within time.
Requirements: Apache or nginx server, MySQL