Google Books is one of Google services that specializes in collecting books which are stored in digital formats.
So far the service has stored millions of books.
All of them are available for public to read.

However, reading books at the Google Books website is uncomfortable.
Magazine, fiction, non-fiction, health, computer, programming, you name it.
Features and Highlights
Google Books Downloader has a humble appearance.

It is plain and simple.
The top side is where the input box is located.
The book will be saved into the desktop by default.
Google Books Downloader saves each book in PDF format unless you change it to other format.
There are three file formats it supports, which are PDF, JPEG, and PNG.
The file format that you select will affect the file size of the downloaded books.
Google Books Downloader offers only very few features.
There is no tool to manage the downloaded books or a reader to open them.
Both are free and good.
Unfortunately, despite how small it is, there is no portable version.