Pencil (32-bit)

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.

Features and Highlights

Easy GUI Prototyping
Pencil provides various built-in shapes collection for drawing different types of user interface ranging from desktop to mobile platforms. Starting from 2.0.2, Pencil is shipped with Android and iOS UI stencils pre-installed. This makes it even easier to start prototyping apps with a simple installation.

Built-in Shape Collections
Starting from 2.0.2 the app has even more shape collections included by default. The list of built-in collections now includes general-purpose shapes, flowchart elements, desktop/web UI shapes, Android, and iOS GUI shapes. There are also many other collections created by the community and are distributed freely on the Internet. You can easily grab a collection and install it into the tool with a simple drag-and-drop operation.

Diagram Drawing Support
The program now supports connectors which can be used to "wire" shapes together in a diagram. A collection of flowchart shapes are also available for drawing diagrams.

Exporting to Different Output Formats
This tool supports outputting the drawing document 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. The software also supports exporting documents into popular formats including OpenOffice/LibreOffice text documents, Inkscape SVG, and Adobe PDF.

Easily Find Cliparts from the Internet
The product has a clipart browser tool that integrates with OpenClipart.org to let users easily find cliparts by keywords and added them into the drawing by a simple drag-and-drop operation. Clipart listed by the tool is in vector format and hence good for users in scaling to appropriate sizes.

Inter-page linking
Elements in a drawing can be linked to a specific page in the same document. This helps the user define the UI flow when creating an application or website mockups. Linkings defined in a document are converted into HTML hyperlinks when the document is exported into web format. This process creates an interactive version of the mockup in which viewers can see a simulated flow when clicking on the UI elements.

Also Available: Download Pencil for Mac