Short drawing programme
Processing - 93 · 0.9 = 83.7

With next to no overhead for drawing, but a very verbose syntax, in Processing the best score is probably reached without any nice features and only one bonus:

void setup(){
size(600,400);
}
void draw(){
if(mousePressed)line(mouseX,mouseY,pmouseX,pmouseY);
}


Score: 93 · 0.9 = 83.7 (Newlines are for readability only and are not counted in the score.)

However, it's much more fun with all the bonuses in place:

void setup(){
size(600,400);
}
int i,x,y;
void draw(){
stroke(7*i%256,5*i%256,i%256);
strokeWeight(i%9);
if(keyPressed)i++;
if(!mousePressed){x=mouseX;y=mouseY;if(x&lt;0)background(0);}
}
void mouseReleased(){
line(x,y,mouseX,mouseY);
}


Score: 221 · 0.8 · 0.7 · 0.9 = 111.4

It's used like this:


Click and drag the mouse to draw a straight line.
While clicked, drag the mouse off the left side of the window and release the mouse button to clear the screen.
Holding down any key will cycle through the red, green and blue values of the drawing colour and through different stroke thicknesses. Since the cycling periods are different, practically all combinations can be reached (with a bit of trying).




Edit:

Since freehand drawing gives the 0.7 bonus as well, here is yet another solution:

void setup(){
size(600,400);
}
int i;
void draw(){
stroke(7*i%256,5*i%256,i%256);
strokeWeight(i%9);
if(keyPressed)i++;
if(key&gt;9)background(0);
if(mousePressed)line(mouseX,mouseY,pmouseX,pmouseY);
}


Score: 188 · 0.8 · 0.7 · 0.9 = 94.8

It's used like this:


Click and drag to draw freehand lines.
Hold the tab key to change the colour and stroke thickness. This can also be done while drawing (see picture).
Hit any key but tab and then tab to clear the screen.