BookWalker has a new option for people who have created a free account (or you could log in using Yahoo ID, Facebook, etc.). There are thousands of books, manga, light novels, etc. that are available for 10-minutes. Unlike 試し読み, which is usually the cover and first ~10 pages, in this case you are allowed to read as much as you want of a book within a 10 minute period per day.
The books are tagged like this:
Once you have logged in (if you hadn't already) the book opens and you have 10 minutes to read. You cannot download, but if you click at the top of the screen you will get a menu that includes a clickable table of contents.