What device resembles a pen and can "write" on a screen?

The stylus is the device that resembles a pen and is specifically designed to interact with touchscreens. It allows for precise input on devices such as tablets or smartphones, making it ideal for drawing, handwriting, or selecting small on-screen elements. The design of a stylus typically mimics that of a pen, which provides a familiar and comfortable way for users to input information or create art on digital devices.

When using a stylus, users can achieve more accuracy than fingers alone, especially for tasks that require detail and finesse. This capability enhances the user experience for applications that involve graphic design, note-taking, or applications that benefit from drawing to express ideas visually.

In contrast, other devices like a touchpad, trackball, and mouse serve different purposes. A touchpad involves finger movements to control the cursor, a trackball uses a rolling ball to navigate, and a mouse, while more versatile in many ways, does not provide the pen-like precision and interaction that a stylus does. Thus, the stylus stands out as the most appropriate answer to the question about a pen-like device that can "write" on a screen.