miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
SpeedTree - SpeedTree is a powerful toolkit used to create 3D vegetation for video games, films, and animations.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
The Grove 3D - Model or grow adaptive 3D Tree models for use in CG renderings.
Paint XP for Windows 7 - Standalone old MS Paint program that allows you to get your old XP Paint interface in Windows 7.
Tree Studio - Easy 2D Tree Creation