This is a great text editor for writing articles, books, diaries, and notes. It's free, simple, and functional.  To use this app, you just need to install it, then open your document, and you're done.

There are two modes available in this app. You can edit your document or view it in the default mode. In either case, you can add a date, title, and other information to the document to help you remember it better. 

You can save your document in two different ways. You can save it as a text file or a zip archive. The latter is more useful since it allows you to protect the document with a password.  This app supports automatic scheduled backup to Google Drive and DropBox.