The initial source comes from https://github.com/sdcuike/issueBlog/issues/4

http://greenteapress.com/wp/

https://papers.nips.cc

https://github.com/PacktPublishing free to download books code by Packet

https://github.com/EbookFoundation/free-programming-books Very immense

http://www.ituring.com.cn/book?tab=free Turing free books

http://www.it-ebooks.info

http://ebook3000.com/Programming/index.html Not just it ebooks, including other areas, has ads

http://smtebooks.com BAD

http://ebook-dl.com Either download or see films, interesting

https://scanlibs.com BAD ! download interval time is restricted

http://www.java1234.com/a/javabook/ Chinese site

https://www.iteblog.com/archives/category/ebooks/ focus on big data

https://www.packtpub.com Publisher

https://www.packtpub.com/packt/offers/free-learning One free book per day

http://www.oreilly.com/data/free/archive.html

http://bookboon.com/en

https://www.pdfdrive.com Very Good ! many areas

http://www.finelybook.com

http://www.tradepub.com

http://www.jb51.net/books/

http://www.itebookshare.com/

http://www.ebook-daraz.com/

http://www.javazhijia.com/sj/

http://ebook3000.com/Programming/index.html

https://foxgreat.com/

-http://www.0daydown.com/

http://proglang.informatik.uni-freiburg.de/teaching/concurrency/2014ws/

http://www.colorado.edu/cs/computer-science-course-archive

http://www.topitbooks.com/

http://mindview.net/Books/DownloadSites/

http://inventwithpython.com/#invent

http://greenteapress.com/wp/

http://www.mhprofessional.com/

http://hackr.io/

https://github.com/justjavac/free-programming-books-zh_CN

http://www.ituring.com.cn/book/ebook

https://www.ebooks-it.net

http://itmanagersinbox.com/1875/13-sites-to-download-free-ebooks/

http://www.tcpipguide.com

http://www.lemis.com/grog/Documentation/Lions/

http://www.tcpipguide.com/free/t_TCPConnectionTermination-2.htm

http://www.freesoft.org/CIE/Course/Section4/11.htm

https://landing.google.com/sre/book/

https://bushkarl.gitbooks.io/spring-cloud/content/

http://www.sonatype.org/nexus/resources/resources-book-links-and-downloads/

https://books.sonatype.com/mvnref-book/reference/index.html

http://book.huihoo.com/maven-the-definitive-guide/index.html

http://www.commandprompt.com/ppbook/ Practical PostgreSQL

http://use-the-index-luke.com/sql/table-of-contents SQL Performance Explained

http://math.hws.edu/javanotes/

http://aosabook.org/en/index.html The Architecture of Open Source Applications