Holy Grail of Free Programming Books on the Internet
Not sure if it has been seen before, however this is a pretty comprehensive list of all things programming. Has languages I haven't even heard of before, books on algorithms and other Discrete Mathematics, Graphical Processing, Networking, AI, and others. I haven't gotten to really delve in to deep yet ,but a lot of what I have been using for the languages I am learning I'm seeing so should be pretty useful.

Link - Download the Ebooks (Link to Github)