There are two software products named Pencil, that are not related to each other. This article is about the graphical animation software.

1. A 2D graphical
   2D computer graphics
   2D computer graphics is the computer-based generation of digital images—mostly from two-dimensional models and by techniques specific to them...
   
    animation software that runs on Mac
   Macintosh
   The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...
   
   , Windows
   Microsoft Windows
   Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
   
   , Linux
   Linux
   Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
   
    and BSD
   FreeBSD
   FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...
   
   . It has also been ported to the Pandora
   Pandora (console)
   The Pandora is a handheld game console designed to take advantage of existing open source software and to be a target for homebrew development...
   
    handheld.http://pandorawiki.org/Pencil.
2. A GNU free wireframe tool available both as a Firefox plugin and a standalone application http://pencil.evolus.vn/en-US/Home.aspx.

Pencil uses a unique bitmap

Bitmap

In computer graphics, a bitmap or pixmap is a type of memory organization or image file format used to store digital images. The term bitmap comes from the computer programming terminology, meaning just a map of bits, a spatially mapped array of bits. Now, along with pixmap, it commonly refers to...

/vector

Vector graphics

Vector graphics is the use of geometrical primitives such as points, lines, curves, and shapes or polygon, which are all based on mathematical expressions, to represent images in computer graphics...

 drawing interface to produce simple 2D graphics as well as animation

Animation

Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. The effect is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in several ways...

.

Pencil is written in C++

C++

C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...

 and is Qt

Qt (toolkit)

Qt is a cross-platform application framework that is widely used for developing application software with a graphical user interface , and also used for developing non-GUI programs such as command-line tools and consoles for servers...

-based. The application license is GNU General Public License

GNU General Public License

The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....

. It started as a simple "pencil test" program by Patrick Corrieri, extended to the current Pencil application mainly by Pascal Naidon.