prototyping and diagramming tool
Pencil Project is a prototyping and diagramming tool with built-in shapes for flowcharting, mobile/desktop/web UI, Android and iOS GUI and more.
Pencil Project Portable works best with the PortableApps.com Platform
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. It includes built-in shapes collections for popular mobile (Android and iPhone) and desktop (Windows and generic) UI designs as well as flowcharts and common shapes. Additional stencil collections and clipart can be easily added as well. Pencil supports connectors which can be used to "wire" shapes together in a diagram along. Pencil project also supports exporting to PNG, web page, PDF, SVG and Open Document formats.
Additional Stencils: Additional stencils can be added by creating a new directory for the stencil set in your PencilProjectPortable\Data\profile\Pencil\Stencils directory and unzipping the collection to that new directory. Pencil Project will detect it as it starts up.