Pencil is built for the purpose of providing a free and open-source GUI prototyping tool that people can easily install and use to create mockups in popular desktop platforms. Pencil provides various built-in shapes collection for drawing different types of user interface ranging from desktop to mobile platforms. The list of built-in collections now includes general-purpose shapes, flowchart elements, desktop/web UI shapes, Android and iOS GUI shapes.
Elements in a drawing can be linked to a specific page in the same document. This helps user define the UI flow when creating application or website mockups. Connectors can be used to ‘wire’ shapes together in a diagram. The drawing document can be stored into different types of formats. You can have your drawing exported as a set of rasterized PNG files or as a web page that can be delivered to the viewers. Pencil also supports exporting documents into popular formats including OpenOffice/LibreOffice text documents, Inkscape SVG and Adobe PDF.