There are many resources available online where you can find free books and other reference materials about food ordering systems. Here are some websites that you might find useful:
1. Google Books - This is a great place to start looking for free books about food ordering systems. You can search for specific keywords or phrases related to your topic and find a wide range of books to choose from.
2. Open Library - This is another great resource for finding free books online. You can search for books by title, author, or subject, and then download them in a variety of formats.
3. Project Gutenberg - This is the oldest digital library that provides free eBooks. It has a vast collection of over 60,000 eBooks in its repository that can be downloaded for free. You can search for books related to food ordering systems and download them in various formats such as PDF, ePub, and Kindle.
4. Online research databases - Many universities and libraries offer online research databases that provide access to a variety of academic journals, books, and other resources related to food ordering systems. You may need to have a valid library card or an institutional login to access these databases.
5. Online forums - Joining online forums related to food ordering systems can also be a great way to find free resources and connect with other researchers and experts in the field. You can ask for book recommendations or share your own research findings with others.
Remember to always check the credibility and reliability of the sources you find online before using them for your thesis.