My all-time favorite program for writing and research projects. It's light on formatting and layout features, but doesn't care. What it's meant for is writing, writing, and more writing. And organizing that writing (as well as all the background info and research you accumilated, and characters, and...) in a clear, concise, effortless way. It also has export formats in place for screenplays.
Give it a shot. If you like the minimalist writing approach without the research and filing features, then also check out Writeroom.