(This was written within the last couple of years)
If I could design my own writing software, it would merge RoughDraft and Writer’s Cafe.
RoughDraft is a word processor that has tabs (great for multiple projects/chapters), auto-save to rtf, text pad on the side. Had presets for manuscript and screenplay writing.
Writer’s Cafe is a planning tool. There’s a “journal”, where you can just jot notes. There was a second “journal” that allowed you to post by date. There was an area to create storyboards via virtual cards; and an area to store clips and links from research. It had a built-in dictionary/thesaurus, writing prompts, and a timed write function.