The initial source comes from sdcuike/issueBlog#4
https://github.com/PacktPublishing free to download books code by Packet
https://love2.io Chinese site
https://github.com/EbookFoundation/free-programming-books Very immense
http://it-ebooks.directory Access slowly in China mainland
https://inspirit.net.in/ebooks Good resources
http://www.ituring.com.cn/book?tab=free Turing free books
http://www.epubit.com.cn/book?tab=ebook&sort=free Chinese e-books community, seems to be dedicated to translating English books to Chinese, so many are not free
http://www.allitebooks.com/ Fabulous
http://bestcbooks.com Chinese site
http://ebook3000.com/Programming/index.html Not just it ebooks, including other areas, has ads
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
https://www.pdfdrive.com Very Good ! many areas
http://ebook3000.com/Programming/index.html
http://www.java1234.com/a/javabook/
http://proglang.informatik.uni-freiburg.de/teaching/concurrency/2014ws/
http://www.colorado.edu/cs/computer-science-course-archive
http://mindview.net/Books/DownloadSites/
https://u14147674.ctfile.com/u/14147674/27350776
http://yun.baidu.com/share/home?uk=2214641459#category/type=0
http://pan.baidu.com/share/home?uk=3339153721&view=share#category/type=0
http://pan.baidu.com/share/home?uk=3241811474&view=share#category/type=0
http://vdisk.weibo.com/s/zJQeg4_RkvSaa
http://pan.baidu.com/wap/share/home?uk=2399537899&third=0
http://www.java17.com/resources/
http://vdisk.weibo.com/u/3215987620尾盘
http://www.pan1234.com/index.html
http://www.pan1234.com/index.html
http://inventwithpython.com/#invent
http://www.mhprofessional.com/
https://www.gitbook.com/explore
https://en.wikibooks.org/wiki/Subject:Computing
https://github.com/justjavac/free-programming-books-zh_CN
http://www.ituring.com.cn/book/ebook
http://itmanagersinbox.com/1875/13-sites-to-download-free-ebooks/
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/
https://github.com/eacdy/spring-cloud-book
https://www.gitbook.com/book/waylau/rest-in-action/details
http://www.sonatype.org/nexus/resources/resources-book-links-and-downloads/
https://books.sonatype.com/mvnref-book/reference/index.html
https://github.com/es5/es5.github.io
http://git.oschina.net/progit/
http://book.huihoo.com/maven-the-definitive-guide/index.html
http://docs.oracle.com/javase/tutorial/essential/concurrency/imstrat.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://www.brpreiss.com/books/opus5/index.html
http://blog.jobbole.com/5200/国外程序员推荐的免费编程书籍资源
https://www.gitbook.com/@neomatrix369
http://aosabook.org/en/index.html The Architecture of Open Source Applications
http://www.ituring.com.cn/article/13057
https://www.coursera.org/course/progfun
https://leanpub.com/rest-assured-with-jaxrs
http://xclient.info/?t=8b0a8b2b8a52c958b62c34f5c4437a457cd119fd
http://www.cgtsj.com/software/maya/
http://www.meijutt.com/search.asp
http://www.ygdy8.com/html/gndy/dyzz/index.html
http://www.d1money.com/dianzishu