The Torque 3D engine from Garage Games became open source pretty recently and I have to say it's a pretty nice game engine. Though it's not my favorite it's definitely a great engine to use if you want to make a shooter. They've got guides and there's some pretty good books on it too.
I recently got a copy of the Torque 3D Game Development Cookbook. I really liked the book. It's put together in a "recipe" format (hence the "Cookbook" in the title). Each recipe focuses on a different specific task. One chapter has a bunch of recipes for string manipulation and string processing which I found quite useful. It isn't exactly a step by step project oriented book. Most game engine books focus on the basic topics needed to complete a project at the end of the book, but this one serves as a great reference instead. Most of the recipes are fairly stand alone too so you can read them in whatever order you want. If you want to learn Torque 3D then I would suggest going through the guides on the Torque website first.