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
Pencil is a powerful tool primarily focused on vector graphics and detailed illustrations, making it suitable for more advanced users. In contrast, Tupi is designed with beginners in mind, offering user-friendly features and mobile support, but lacks some of the advanced capabilities of Pencil.