The Pencil Project's unique mission is to build a multi-platform free and opensource tool for making diagrams and GUI prototyping that everyone can use.
Builds are available for Windows, Mac, Linux, and as a Firefox extension
Project was originally sponsored by a Viatnamese site, Evolus, with code on googecode. That has not been updated since 2013, and new builds are occurring on an actively maintained fork on github.
These details are provided for information only. No information here is legal advice and should not be used as such.