Pencil is an open-source GUI prototyping tool that's available for ALL platforms. Pencil is built for the purpose of providing a free and open-source GUI prototyping tool. Developed by Pascal Naidon and Patrick Corrieri
License: Open Source
sK1 is a powerful vector graphic design tool with multi-page support and advanced color management, ideal for professional designers. In contrast, Pencil is more user-friendly, suited for quick sketches and animations, but lacks the depth needed for high-end vector graphics work.