The Debian Administrator's Handbook
The Art of Unix Programming
Quakenet/#php Tutorial - German/Deutsch
Street-Fighting Mathematics
The Linux Command Line
97 Things Every Programmer Should Know
An Introduction to Programming in Go
Free Software, Free Society
Linux Kernel in a Nutshell
The Haskell School of Music
Learn You a Haskell for Great Good
Learn You Some Erlang for Great Good!
The Cathedral and the Bazaar
PC Assembly Language
Learn Python the Hard Way
A Byte of Python
why's (Poignant) Guide to Ruby