very good CAD software
Pencil2D is a cross-platform animation/drawing application.
Simple drawing program for Linux
Easy and smart classic color picker
A hybrid graphics editor and programming environment
ARO helps physically disabled students to create mathematical drawings
Canvas drawing program with recording and animation
OBSOLETE; try http://drawpile.net/ instead!
dedalo is a 2d cad drawing software written in python3.
2 players drawing program
Drawing app built with C#
A multiuser web-site for drawing and conversation.