My big project du jour is a novel, set in a near-future dystopia. The novel has three main characters, each coping with the end of their world in different ways. The chapters alternate from character to character, showing their respective journeys.
The novel has its roots in a short story I wrote that features only one of the characters. Like any piece of writing, the story has changed a lot in the months since I started it. For the first five months I wrote sequentially, chapter 2 after chapter 3, etc. In recent months, I took the novel apart and started working each arc separately. When I finish all three arcs, I'll braid it all together again and should have a 66-chapter, 300-odd-page draft.
To help me keep things straight, I put a color-coded chapter list on the Whiteboard above my desk, with a one- or two-word reminder of important events in each chapter.
If nothing else, it reminds me that I've come a long way — and still have a fair hike ahead.