Pencil is a free, multiplatform tool designed to create visualizations of prototype graphical interfaces (GUI) of websites, programs, etc. Creation of each application should begin with the preparation of the basic concept of the program as well as the graphical interface, which should be transparent and as functional as possible for the user. Instead of sketching projects on a sheet of paper, we will be helped by the free Pencil program, which allows us to prepare a fast and effective prototype of the GUI interface for our application.

Pencil offers a wide range of shapes to create designs. Apart from arrows, squares and other basic shapes we can also find here GUI elements (buttons, menus, checkboxes, tab panels, progress bars, etc.) used by Windows XP, GTK environment, standard web interface elements or a collection of high quality shapes used by iOS (iPhone, iPad) and Android (phone, tablet) platforms. Additionally, on the project page you can find a number of shapes and GUI elements designed to create, among others, interfaces for the Dojo Javascript Toolkit environment.

Using Pencil, we can also create diagrams demonstrating how the application works or how to think and solve problems resulting from the complicated functionality of our application or idea.