Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
One of the great things about open source platforms and applications is that skilled authors often put free books online as guides. We've written about excellent ones for Ubuntu, one for Linux hacks, and one for the GIMP graphics application. Recently, I came across a great, free online book on the super powerful open source 3D graphics and animation application Blender. The book is called Blender Basics, Second Edition, and while it has the slight shortcoming of showing examples from Blender version 2.4 (Blender is now on version 2.48) it's still an excellent, very thorough way to learn the application. If you're unfamiliar with Blender, it's so flexible that impressive, full-length animated movies have been created with it. Here's more on what's in the book.
Blender Basics is a 120-page PDF, and it takes about a minute to download the whole book. The book consists of 21 chapters on everything from setting up worlds, to rendering characters, to raytracing and adding lighting effects. The 21 chapters are followed by many screenshot-driven practice sets where you can learn to build impressive characters, set up and light up worlds, and more.