Pencil Project is an open-source GUI prototyping tool. Developed by Evolus
License: Open Source
Pencil Project is an open-source tool that excels in creating wireframes and mockups with a user-friendly interface, while Gliffy is a cloud-based diagramming tool known for its real-time collaboration and extensive shape library. The choice between them depends on whether you prefer a free, customizable solution or a more polished, collaborative environment.