
When writing a book, the first rule is to, well, write. Naturally, writing requires some type of word-processing software.
The granddaddy and probably the most familiar word-processing program is Microsoft Word. It includes some wonderful tools, such as an inbuilt spell-checker, grammar checker, etc. It can even read your words back to you out loud. (Which, incidentally, is a fabulous editing tool. If you’re prone to typing double words, hearing them read back to you will smack you right between the eyes.)
Free Options
Free office suites and standalone word-processing programs also work perfectly well to write text content, such as LibreOffice (formerly Open Office), WPS Writer, and even Google Docs.
Author-Specific
Other text editors are geared for use by authors. They help with targeted work elements such as character management, grammar, images, etc. Among them are Scribus (which will also format your book), Manuskript, and GhostWriter. When working with complex works, such as non-fiction books requiring indexes and other details, one of the author-centric programs is most likely your best bet.

