The latest stable version of Pencil is 1.3 and can be installed using the following options:

1. Option 1:

   Use as a Firefox addon.

   Pencil can be installed into Firefox 4+ as an addon. After being installed, Pencil can be launched by using its own menu entry in the Firefox Tools menu.

   Install the latest version(Version 1.3.4, xpi file, ~ 1.8MB)

    
2. Option 2:

   Run as a standalone application.

   Thanks to the XULRunner project which provides Pencil a way to run completely outside Firefox. XULRunner builds of Pencil 1.2 are available for the following platforms:

   GNU/Linux

   • Fedora 11/12:
     evolus-pencil-1.2-0.i386.rpm  (~ 500 KB, requires xulrunner-1.9 or above)
      
   • ArchLinux:
     available as a package in AUR   (maintained by tinhtruong)
      
   • Other GNU/Linux:
     Pencil-1.2-0-linux-gtk.tar.gz  (~ 500 KB, requires xulrunner-1.9 or above)

   Windows

   • Windows XP/Vista and 7:
     Pencil-1.3.4.win32.installer.exe   (~15.5 MB, using private xulrunner)

   MacOS X

   Pencil-1.3.4-OSX.dmg   (~32 MB, using private xulrunner)