I’m very keen on using disposable fountain pens. I like the line quality and don’t care if the odd pen or two goes missing (due to increasing absent-mindedness).
This problem extends to frequently leaving a pen down without its cap and then finding that the ink has solidified.
Today’s invention is therefore a fountain pen which gradually recaps itself, using a mechanism like these bathtoys.
If you put the cap on the non-nib end when writing, the string just pulls taught.
Leaving the pen down uncapped results in gradual recapping (after a period determined by shortening the string to one’s preference).
This also has the benefit that the cap is harder to mislay (It might actually be better if the string were replaced by a band like a spring-loaded tape measure).