Browser based Canvas UI?

[Ken Seehart]

A couple years ago I stumbled upon an interesting technology but I can't 
seem to find it, and I can remember what it is called.  Unfortunately 
this makes it difficult to search for.  I am am aware of several partial 
matches (items that meet a subset of the requirement listed below).  
Does anyone know what does /all/ of the following?

1. Works on at least FF and IE on XP and Linux out of the box, probably 
others

2. Does not require /any/ plugin download at all of any kind to view 
(this disqualifies flash, svg, silverlight, java, and others)

3. If you go to the web page for the first time on a freshly installed 
operating system, without admin privileges, you will see the 
functionality listed below immediately, and with no downloaded plugins 
and installers.  (I apologize for the redundancy, but I want to 
preemptively avoid a flood of non-applicable responses).

4. Graphics, including sprite animation

5. Dynamic response to mouse motion: dragging sprites for example

6. Programmable in Python, of course

Hints from what I can recall:
- Built from javascript as it's raw material under the hood (after all, 
it can't very well be anything else given requirements 1,2,3)
- Seems quite magical since I didn't know the necessary graphical raw 
materials existed in javascript
- I think it's based on Ajax, but I can't seem to find a relevant python 
demo of it due to too much clutter in my google searches

Ken