When I think about tools, I think about Ken Wood. He designed an ingenious foundation project in which sculpture students had to design and manufacture unique drawing and painting tools. The result was my dream set of beautiful objects begging for experimentation.
Very generally, marks tend toward visual speed and direction whereas shapes tend de-emphasize origin. Marks are immediate and shapes are more logical and planned.
Currently, I consider shapes over-sized marks. I love to pry open the mark/shape boundary and experiment using indirect marks (prints of marks), spontaneous shapes and masks. Sometimes the viewer will only be able to appreciate the mark as shape or visa-versa on close inspection.
Often my own mark making is born from accidents. One of my favorite mark making tools is a hank of yarn wrapped rolling pin dipped into ink. I found this “tool” accidentally at a shabori workshop. While I was pole dying, my PVC tube fell across a wet cord, picked the cord up, and offset the pattern as it rolled accross the floor. It was so immediately beautiful, spontaneous and continuous, I have used this technique again and again to make soft pattern grids, to build up value and texture.