A quill.

A friend with whom one communicates using letters, usually over a long distance.

a laser pointer

A liquid polymer delivery system with a form factor similar to a standard ink pen. The polymer is electrically conductive and rapid-drying. Used to create or repair conductive traces on printed circuit boards.

plural of pen pal

A pen, often with a thick tip made of felt.

(computer hardware) A pen-like device allowing a computer user to interact with the screen display.

(idiomatic) A mistake in handwriting.

plural of pen test

(computing, informal) A penetration test.