Stitches is an open source HTML5-powered application for creating CSS sprites on the fly.

With the help of a couple HTML5 APIs, images can be drag 'n' dropped and the sprite image + CSS rules are instantly generated.

It uses Modernizr to check for drag-and-drop, FileReader, and canvas support (which are currently available only in Firefox and Chrome).

A must-bookmark tool for saving time on creating sprites specially when there are too many images to merge.

Designers/developers usually know the frequently-used CSS properties by heart.

However, it is always handy to have a good documentation for easily remembering the rarely-used or new (CSS3) ones.

InstaCSS is a very simplistic website that offers a great documentation of CSS properties without any distractions; a list of the properties, a search engine and user-friendly description of each property.

There are also examples for each item and a chart of supporting browsers.

Simply, InstaCSS is a must have resource for anyone coding CSS.

The Goldilocks Approach is a boilerplate/starting point for creating responsive websites.

It offers a slightly different practice from the most other responsive design frameworks which is: "targeting every resolution/device rather than only the popular ones".

The boilerplate uses a combination of ems, max-width, media queries and pattern translations to consider just three states:

• multi column (too big space)
• narrow column (too small space)
• single column (just right space).

which allow the designs to be resolution independent.

It includes a HTML file, 2 well-commented CSS files (with nice typographic defaults -including print contexts-) and Modernizr.

Responsive web design is being implemented more and more every day + new resources easing the process are being created regularly.

Amazium is a CSS framework that handles the most tricky and time-consuming parts of creating responsive websites.

The framework has a 960px grid with 12 columns and styles for typography, tables, buttons, lists, images and videos, all adjusting their sizes according to the browser sizes.

There are 4 main media queries:

• all browsers over 960px
• iPad or other tablet Portrait (728px)
• iPhone or mobile Portrait (300px)
• iPhone or mobile Lanscape (420px)

As a bonus, Amazium includes a ready-to-use 404 page as well.

MQFramework is a responsive CSS framework that uses the @media property (media-queries) and works perfectly on major screen sizes down to mobile.

The framework is based on a 12 column-grid and includes a typography stylesheet to handle the basics and a CSS reset.

It is simply a core for building responsive websites which you usually wouldn't need to change any part of but add your own styles on top of it.

MQFramework is a very easy to  implement and there are 2 versions provided to choose from: fluid + fixed.

Gridlover is a free to use web application for creating a type system with modular scale and vertical rhythm.

Inside a page with major HTML tags for type like headings, lists, paragraphs or article, it allows playing with values like:

• body font size
• body line height
• scale factor
• sizes for each element
• the unit desired (px, rem or em)

and keeps everything tidy by scaling them accordingly. Once you are set, it outputs the generated CSS rules for use.

Transitions in CSS3 brings many possibilities on animating and morphing HTML elements.

Lea Verou is sharing a beautiful experiment and resource -Animatable- that showcases different CSS transitions (and how simple they are).

Each transition is applied to a box where you can activate by hovering them (or run the transitions for all items).

You can also click the items to easily see the "from" and "to" values of CSS properties changed.

LESS is a great language for writing styles faster and getting more out of CSS with its dynamic nature (variables, mixins, operations and functions).

Normally, .less files are live-converted to CSS via JavaScript by the browser (or server -like Node.js-).

SimpLESS brings another option for designers willing to generate the CSS from .less files quickly.

It is a desktop-app that has versions for Windows, Mac OS X + Linux and works simply by drag 'n' dropping your project files into the app and getting the CSS output.

P.S. SimpLESS is also an open source project.

Codrops, a web development blog publishing very nice tutorials, has released a set of creative navigation examples built with pure CSS(3).

There are 10 unique examples, all have the same HTML structure but different CSS styles that make use of CSS transitions and animations.

Icons used are from a symbols typeface, so, no images are used in the examples but only HTML, CSS and a custom font file.

They are definitely beautiful "as is" and also a good starting point to create new ones.

Foundation is a very impressive and feature-rich framework for quickly prototyping + creating the production code.

The framework is responsive, works smoothly on all major browsers (including mobile) and completely open source.

It has styles for typography, links, lists, forms (with custom radio buttons, select lists and checkboxes), tables and buttons.

There is a 12 column, semi-liquid grid which works with all screen sizes and encourages building a single website for all devices.

Foundation also includes Orbit (for content sliding) and Reveal (for modal dialogs) that both are powered with jQuery.

This is definitely an exciting project for building modern websites easily and it is a good alternative to the recently launched yet popular Twitter Bootstrap.