Webapplications need to be enriched. A couple of months ago I thought what we had back then was about as rich as we could get, but since Google started to write rich web applications I believe we can do a lot better than what we're doing right now. Have a look at Gmail and the very recently launched Google Suggest (which has "query completion" as you type). Those are cool, right? Why don't your web applications work as smooth as that? Because writing web application sucks when it comes to client-side stuff.
Yes it's a shitload of work to find a comfortable implementation of each of the different widgets you'd want, but if it'd be open source, each can make its contribution. These are a couple of widgets that I think would be useful:
- A WYSIWYG editor, and if WYSIWYG isn't supported in the browser a good textarea with HTML buttons on top to make manually typing HTML barable.
- Tabset, quickly switch between different tabs. I can imagine loading the content of all the tabs upfront or lazy-loading them (i.e. loading the content the first time the tab is clicked).