Project VolamirEarly 2003 saw an attempt at creating a purely browser-based MMORPG. While pretty much impossible at the time a valient effort was made nonetheless (eventually resorting to Flash as a client), sadly yielding little result.
FMS (link)A CMS build by FragFrog - hence Frog's Management System. It uses AJAX to allow a real-time preview of edits and the ability to edit content in place. Imagine simply double-clicking a page, rewriting part of the text and clicking away again to store it. Moreso, simply entering an URL sufficed to create a page (a concept inspired by Piter Pasma) allowing you to create content on-the-fly. Spambots apparently found it a true haven for dumping all kinds of advertisements easily, and hackers used the file-upload functionality excessively till I put the entire system behind a login. It is the most userfriendly content management system I have seen to date, though it never made it to a production environment.
GaME (link)To simplify the management of a Mangos server (most commonly used to host private World of Warcraft servers) I wrote a client-server package in JAVA called Gamemasters Mangos Editor. It uses serialized objects as main form of communication between the client (GaMEC) and server (GaMED), while the server in turn utilizes SOAP to communicate with the Mangos service. It allows real-time modification of game and user parameters, such as editing a creatures parameters, sending in-game mail or disconnecting and banning a user.
Development has been on hold for a few months as I have had very little time to invest in it, though chances are good I will be able to work on it again soon.
Fai (link)Fai was writtin in a week or two long before I even thought about studying artificial intelligence. It is in essence a chatbot based on statistical text analysis. What makes Fai marginally smarter than your average chatbot is her ability to learn and her crawler, capable of analysing thousands of websites per hour to obtain new word definitions and meanings. Her RSS reader furthermore gives her the ability to keep abreast of recent developments. Using simple word analysis algorithms, the meaning of pronouns can be extracted from texts allowing her to answer questions directly, yielding such gems as:
[FragFrog] What is orange? [Fai] I think Orange is the New Pink - see http://www.rcjobs.com for more info! 
(The number in brackets behind her response is the score of that particular response. Users can increase or decrease the score of a sentence depending on whether it is more or less correct).
Project Utgard (link)Following in the footsteps of Volamir, project Utgard is an attempt to create a 3D MMORPG using nothing more than a browser. The Canvas element has a 3D context (that is to say, it will obtain this ability as soon as new browsers support it) making this quite possible. Unfortunately, possible is not entirely the same as attainable and without more help this project is currently on an indefinite hiatus.
As of writing, the only browser capable of both the latest WebSockets as well as the 3D canvas context is Google Chrome's development release, so your mileage may vary.
Project Holmgard (link)Similar to project Utgard but less ambitious is project Holmgard. Using the Canvas and WebSocket elements to be introduced with HTML5, this is in essence an attempt to recreate the game Warcraft II. So far most core functionality (walking, attacking, displaying backgrounds and units, scrolling, etc) is working but a lot still needs to be done before a release version is completed. And of course then there is the question of whether or not Blizzard has finally obtained a sense of humour, similar projects in the past have been shot down rather abruptly I hear.
As with project Utgard, only the very latest development / nightly builds of Chrome and Mozilla offer support for this at the moment.