GitBook Editor

If you are looking for a web-based publishing platform that enables you to write both Markdown and Asciidoc, all while offering some useful features like proofreading and version control, then GitBook might be worth your while.
But if you want a more direct writing environment, like the one provided by your desktop, then GitBook Editor can offer you exactly that.
In a few words, GitBook Editor is a simple and useful software solution that makes it as easy as possible for you to write and publish your books without many distractions.

Requires a valid GitBook account

If this is the first time you have to deal with GitBook, then you are required to create an account before you proceed. Once logged in, you are met by a simplistic main window that makes it easy for you to create new or manage books both locally or from the GitBook.com platform.
As soon as you open or create a new book, you are greeted by a more comprehensive window that provides quick access to all the app's features, as well as the contents of your books via chapter and file-tree panels.

Swiftly write and edit books using Markdown and Asciidoc

You can edit text from both the top toolbar or with the help of the contextual menu, whatever suits your working style best. The utility also provides you with some advanced proofreading features, like spell-checking and suggestions meant to improve the clarity of your texts.
For example, it can detect errors or overly-complicated phrases and words and propose better alternatives, with support for more than 30 languages. In addition, its built-in history manager enables you to review the changes made before you submit the book for publishing.

Competent publishing utility, but may not be everyone's cup of tea

To conclude, GitBook Editor offers an efficient and straightforward environment for writing, editing and publishing your ebooks, directly from the comfort of your computer's desktop.
We will not go as far as saying it is the easiest and fastest alternative out there, since it does require a bit of working knowledge of Markdown and Git, but once these are mastered, you can take all that is written above about GitBook Editor for granted.