Trimble (formerly Google) Sketchup is a fun tool. When I was playing with it, it was a desktop app. Looks like it still is - but I believe it has a significant ecosystem of plugins and addons and it may support export to Web formats. Might be worth a look.

>I tried most of those with Chrome, Firefox, Opera and IE with mixed results. But they are essentially (good) animation sites - what we need is something more like CAD/CAM functionality. Adding items , grouping sizing, scaling, zooming, rotating, skewing, path manipulation, intersection detection, etc.etc.
>
>This is the closest I've seen so far: http://code.google.com/p/svg-edit/ . A huge amount of clever javascript but still comparatively crude in what it does (and that's only a small percentage of what we would need :-{ )
>
>>I'm not sure what you're doing exactly, but look at these sites done in HTML 5. They may or may not work for you depending on the level of HTML 5 support in your browser.
>>
>>http://worldsbiggestpacman.com/
>>http://www.pirateslovedaisies.com/
>>http://www.endlessmural.com/
>>http://disneydigitalbooks.go.com/tron/
>>http://www.nevermindthebullets.com/?fbid=lFwMzIHSaLv
>>http://www.bmw.com/com/en/insights/technology/efficientdynamics/phase_1/bmwvision_introduction.html
>>http://www.thekillersmusic.com/html5?utm_source=windows&utm_medium=sitemode&utm_campaign=IE9
>>http://www.theshodo.com/
>>http://www.visitnmc.com/
>>http://jsdo.it/event/svggirl
>>
>>>I'm struggling to see how HTML5 can be seen as a replacement for Silverlight for the type of stuff I'm doing (highly interactive graphics)
>>>
>>>The drag/drop functionality helps.
>>>The Canvas element looks good at first sight but, AFAICS, can't be accurately printed and can't be populated from markup.
>>>Embedded SVG may make some things a bit simpler than they were before..
>>>Maybe better dialogs..
>>>Local storage of sorts.
>>>
>>>That's about it. We're going to spend a couple of weeks trying out ideas but I'm not optimistic (and hate javascript with a vengeneance :-{)
>>.