The Internet Archive is a digitization effort, similar to google books, where millions of books have been scanned. You can search easily without an account. Anyone can create a free account, and after doing so, check out a book to read the full-text. BIG CAVEAT: only one person in the world can be accessing that copy at a time.
More information about the project is available here: https://archive.org/about/.
The following information is from the Internet Archive help page - more questions answered here.
What is the loan duration for Internet Archive books?
Most books are available short-term access for 1 hour. Some may allow a longer 14-day loan.
Can I download an encrypted PDF or EPUB of the book?
When patrons check out a book for 1 hour, they can only use it through the web book reader interface. When patrons check out a book for 14 days, they can either read the book through the web book reader interface or download an encrypted file using Adobe Digital Editions - the same technical protection software used by commercial publishers on their ebooks.
The book I want to read is only available for a 1 hour loan, but I can’t read the whole book in that time. Can I renew a book that I have borrowed for 1 hour?
Yes. If there are available copies, patrons can check the book out again.