keyword: Problems, exercises – 0 free books.
These OSI Approved License licensed ebooks are free to read - the people who created them want you to read and share them.
Open source licenses are licenses that comply with the Open Source Definition — in brief, they allow software to be freely used, modified, and shared. To be approved by the Open Source Initiative (also known as the OSI), a license must go through the Open Source Initiative's license review process.
All these books are free to read: either they're distributed with a free license, or they're in the public domain.