Trelby is a completely free and open source screenwriting program. It is currently developed by:
If you want to contact the Trelby development team for any reason, please use the mailing list: http://groups.google.com/group/trelby. Before starting a discussion, please be sure to check the FAQ page first to be sure you're not about to raise a topic discussed many times before.
Trelby was originally known as Blyte, and was written by Osku in 2003-2006 and sold as a commercial program by a company he founded. However, the sales of the program were not enough to justify spending most of his free time working on it, so in 2006 he open sourced it.
The program faded into complete obscurity for five years, until in late 2011, Anil Gulecha found it and started contributing improvements. This resurrected Osku's interest in the program, and he started working on it again as well.
They decided to change the name of the program to Trelby, create a brand new website for it (the one you're on now), bring the code up to date which it needed after five years of neglect, and try to create a development community around it.
The intersection of software developers and screenwriters is tiny, and is probably the reason for the lack of quality open source screenwriters. If you're a part of that tiny group, why not join in?