Vimdiff is pretty popular with checking the difference between codes. A Javascript version, JSBlend came out lately.

JSBlend is such a great tool for any wiki developer or a code repository front end developer. Hope I can see that in Wikipedia and web based svn systems soon.

Remember the classic "Arkanoid"? if you love it, you will love it when it can be played in a browser. The time has come(a long time ago..)--DHTML Arkanoid
I love the feature where you can make your own maps :)

Kris Cieslak created a few JavaScript games using YUI.

Green Felt contain a lot good looking solitaire game created in JavaScript.

Chipbench a Amiga Workbench clone

If you think everything you just saw is impressive, checkout Racing, the first real 3D environment implementation in JavaScript. (Canvascape uses ray casting a semi 3D engine)

Vox Imperium, a Ajax Civilization like strategy game. Players can build units, buildings and capture towns for hours. With the addition of the MapMaker, players can create their customized maps to express their creativity and fight for their dream world at the same time.

Amberjack, a 4KB JavaScript site tour creator. Many skins can apply to Amberjack, here shows an Safari skin:

Amberjack works great as a system to improve user's overall experience and knowledge for any website.