Gliffy

http://www.gliffy.com/

mxgraph

http://www.draw.io/  和 http://www.jgraph.com/index.html

DrawAnywhere

http://www.drawanywhere.com/

FunnyDraw

http://point.mathfan.com/Flash/FunnyDraw/FunnyDraw.swf

Pixlr

http://pixlr.com/editor/?loc=zh-cn

google doc

中的 insert drawing

https://docs.google.com/document