Pencil Project
Pencil is a standalone app or Firefox extension that lets you create diagrams or UI mockups. It doesn't have collaboration/multi-user features. The Pencil Projects unique mission is to build a free and opensource tool for making diagrams and GUI prototyping that everyone can use. Top features: Built-in stencils for diagraming and prototyping Multi-page document with background page Inter-page linkings! On-screen text editing with rich-text supports Exporting to HTML, PNG, Openoffice.org document, Word document and PDF. Undo/redo supports Installing user-defined stencils and templates Standard drawing operations: aligning, z-ordering, scaling, rotating... Cross-platforms Adding external objects Personal Collection Clipart Browser And much more... Pencil can be installed as Firefox extension or as a standalone application for Windows, GNU/Linux and MacOS X
