I've noticed many professional authors swear by 'Scrivener' for its robust organizational features. It allows you to break down chapters, keep research notes handy, and even compile drafts into various formats. Another favorite is 'Ulysses', which offers a clean, distraction-free interface and seamless syncing across devices—perfect for writers who value simplicity and mobility.
For collaborative projects, 'Google Docs' remains a go-to due to its real-time editing and commenting features. 'NovelPad' is also gaining traction for its intuitive chapter structuring and character tracking, making it ideal for long-form fiction. If you're into detailed world-building, 'Campfire Blaze' provides specialized modules for lore, timelines, and magic systems. Each of these apps caters to different aspects of the writing process, so it really depends on your workflow and preferences.