Linux & BSD

Absolute FreeBSD, 3rd Edition
The Complete Guide to FreeBSD
By Michael W. Lucas
Absolute OpenBSD, 2nd Edition
Unix for the Practical Paranoid
By Michael W. Lucas
The Artist's Guide to GIMP, 2nd Edition
Creative Techniques for Photographers, Artists, and Designers
By Michael J. Hammel
Autotools, 2nd Edition
A Practitioner's Guide to GNU Autoconf, Automake, and Libtool
By John Calcote
Blender Master Class
A Hands-On Guide to Modeling, Sculpting, Materials, and Rendering
By Ben Simonds
Book of Audacity
Record, Edit, Mix, and Master with the Free Audio Editor
By Carla Schroder
The Book of GIMP
A Complete Guide to Nearly Everything
By Olivier Lecarme and Karine Delvare
The Book of PF, 3rd Edition
A No-Nonsense Guide to the OpenBSD Firewall
By Peter N. M. Hansteen
Designing BSD Rootkits
An Introduction to Kernel Hacking
By Joseph Kong
FreeBSD Device Drivers
A Guide for the Intrepid
By Joseph Kong
The GNU Make Book
By John Graham-Cumming
How Linux Works 3rd Ed cover
What Every Superuser Should Know
By Brian Ward
Linux Basics for Hackers
Getting Started with Networking, Scripting, and Security in Kali
By OccupyTheWeb
Linux Firewalls
Attack Detection and Response with iptables, psad, and fwsnort
By Michael Rash
Linux Programming Interface
A Linux and UNIX System Programming Handbook
By Michael Kerrisk
Practical IoT Hacking
The Definitive Guide to Attacking the Internet of Things
By Fotios Chantzis, Ioannis Stais, Paulino Calderon, Evangelos Deirmentzoglou, Beau Woods
Practical Linux Forensics Cover
A Guide for Digital Investigators
By Bruce Nikkel
Racket Programming the Fun Way Cover
From Strings to Turing Machines
By James W. Stelly
The Book of Inkscape, 2nd Edition
The Definitive Guide to the Graphics Editor
By Dmitry Kirsanov
The Linux Command Line, 2nd Edition
A Complete Introduction
By William Shotts
Wicked Cool Shell Scripts, 2nd Edition
101 Scripts for Linux, OS X, and UNIX Systems
By Dave Taylor and Brandon Perry
Your Linux Toolbox
By Julia Evans