Pen

Arch has support for digital pen/pencil/paintbrush hardware peripherals.

Some provide basic tap and click functionality only. Some are designed for artists/designers and allow angle and pressure sensitive controls.

Graphics tablets - pens with pads separate from a screen

Pens with a pad separate from the screen are known as Graphics Tablets

Wacom is the primary vendor for digital pen tablet peripherals in Linux.

Touchscreen stylus - pens with touchscreens

Pens which work with touchscreens are known as a stylus. Wacom is the primary vendor for these in Linux.

Crossovers / multi-modal interfaces

Pen and touch based device interaction is a field of heavy development fueled by a mix of the smartphone and computing tablet revolutions along with creative field demands.

Some emergent tools like Weylus allow using a smartphone or touchscreen-tablet (which may support a digital pen) as an interface for another computer.