Windows for Pen Computing is actually an installable component onto Windows 3.1, not a full operating system. It is a set of packages meant for the GRiD tablets, and probably other tablets as well.

As you can see, the desktop is similar, but different.
The Program Manager hasn't changed, but a new program group was added, filled with "Pen Tools". The default background is now a marble image, and the Pen Palette starts up with the system.

Here we have a few of the pen apps, including a notebook that accepts handwriting, an on-screen keyboard, and a form program.

A keyboard and mouse does still function, but you bought Pen Computing for a tablet, right?

The Pen Palette takes in your handwriting, and converts it, as best as it can, to characters that look like this.

"Trainer" helps you with your writing skills. You write in text, and the program checks it to make sure it is readable by the system. If it is not it shows up in the box below.

Of course, there is also a Pen Basics program that teaches you the basic facts about using your tablet, how to write and edit text, and a few other things.