GNU/Linux Desktop Survival Guide
by Graham Williams
While the focus is on free systems in this book it would be unfair not to include some great commercial software. Free open source software may not always serve your needs. You have two options: implement (or pay someone to implement) what you need yourself on top of the base already provided by the open source software; or buy an off-the-shelf solution. The former will give you plenty of kudos in the GNU/Linux world, but the latter might be more practical.
Here we do not delve into the individual products, but rather catalogue what is available.