human
Can you tell me about the different kinds of pens?
assistant
Pens can be divided into two main categories, fountain pens and ballpoint pens. Fountain pens use a small amount of ink in a reservoir inside the pen to write, while ballpoint pens use a thin steel ball that rotates against the paper as it writes. Other types of pens include rollerball pens, which have an ink-filled roller at the tip; gel pens, which use a water-based ink; and felt-tip pens, which use a felt-tipped applicator instead of a steel ball.