"They are four applications designed to serve different
purposes: A web browser, a music player and organizer, another that
does the same for video, and a word processor for screenwriters.
Yet they share one thing in common: All were built with a
Mozilla-based toolkit, either the Gecko Runtime Environment or its
successor, XULRunner. Both toolkits use the same codebase which
"Like Firefox, these applications are free and their code are
released under open source licenses. None is affiliated with the
Mozilla Corporation. Each is backed by an organization that plans
to make money through its software..."