StoryMill is described as 'Storymill is a creative writing tool geared towards book writers; although, it could easily be used for other big creative writing projects, like scripts' and is an app in the News & Books category. There are more than 25 alternatives to StoryMill for a variety of platforms, including Windows, Mac, Online / Web-based, Linux and iPhone. The best alternative is Manuskript, which is both free and Open Source. Other great apps like StoryMill are Scrivener (Paid), Hemingway Editor (Paid), yWriter (Freemium) and oStorybook (Free, Open Source).
Manuskript is an open-source tool for writers, with outliner, character management, plot development, distraction-free editor, etc. Outliner Organize your thoughts and snippets in a hierarchical manner. Organize them as you wish, reorganize them on the go.
yWriter is a writing tool that uses "scenes" as a unit of text and allows you to associate that text with all manner of story elements (characters, locations, items) as well as place it and rearrange it within the context of chapters.
Typely is precise. Existing tools for improving prose raise so many false alarms that their advice cannot be trusted. Instead, the writer must carefully consider whether to accept or reject each change.
Based on the Firefox engine, supports standards, visual storyboarding, production scheduling, publication & international languages MUI support. Free tutorials, videos & wiki are available from the site. There is a very helpful community too.
Looking for a suite of tools for writing your book? This is not just a text editor it does so much more. Organise your story using timelines, planning boards and the snowflake tool, all integrated to make writing intuitive and fun.