oop tutorials

[Saaa]

I want to make a few (5-10?) D OOP tutorials for dsource.
That way I can learn about oop myself and help D, I hope :)

They should thus focus on people who never programmed in an oop style.

Every tutorial should elaborate on the previous one, but on themselves also 
compile into something interesting||useful.
The filler code (not related to oop but necessary to make it a interesting 
program) should not be too complex.

Anybody any idea which kind of program suits best?
The filler code in a ray tracer might just be a bit too complex.