Sigil

Sigil can be used to create, open and edit ePub files, as well as other file types, like plain text or HTML. It is a "what you see is what you get" (WYSIWYG) application, which means that simplicity is one of its key features. You don't need to spend more than a few minutes to learn its controls, so you can start working on your projects right away. What's more, the application is offered under the GNU General Public License, which means that it is absolutely free.

The application looks and feels like a traditional word processor, except for the fact that its user interface is cleaner and better organized. You can spot any option you need instantly and there is no need to go through thick layers of menus for something as simple as changing a heading or a paragraph setting.

The largest part of the user interface is split into three parts, on which you can switch between loaded files, edit them on separate tabs and manage a table of contents. The best aspect of the interface is the fact that it can be customized. You can rearrange the editing area anyway you want, change the colors, hide or reveal options on the toolbar and more.

As previously mentioned, the application allows you to work with ePub, TXT and HTML files. Regardless of the file's format, you can edit it just like a plain text document. What's more, the application allows you to switch between different view modes. You can go from plain text view to a code view or to a preview mode.