I'm working on a Raphael/CoffeeScript IDE:

http://fleetinbeing.net/raffi/

It take's after TileMill, a thrillingly ambitious map-styling tool:

http://developmentseed.org/blog/2011/feb/16/announcing-tilem...

Morphic is a visual IDE (with a true emphasis on "integrated") that originated in Self. Both attempts to port it to javascript are beautiful:

SVG: http://www.lively-kernel.org/ Canvas: http://www.chirp.scratchr.org/blog/?p=34

Check out Protovis for even more inspiration:

http://vis.stanford.edu/protovis/ex/

A number of cool IDE's for Processing.js exist:

- http://sketch.processing.org

- http://sketchpad.cc

- http://jsfiddle.net ( Processing specific example: http://jsfiddle.net/zalun/FZqZN/ )

Wow, this lib looks so freaking cool and thought out. What are your future plans?

Oh it's not my library, but I use it in school and it IS awesome :)