"Blender is the free open source 3D content creation suite, available for all major operating systems under the GNU General Public License," as it states right on the website, http://www.blender.org/. Blender works very much like any of the other big animation programs that you actually have to pay for.
It has many features including a fairly easy to use interface that keeps mostly all the commands out in front where you can see and get to them easily. It also has a setup for people who want to use it for character modeling, it comes with some preset shapes built into the program, for example, you can place a sphere, cube, and other basic shapes to cut out a lot of the time it would take to create them from scratch. Another feature that I think is very useful is the rigging system or in other words it allows you to place 'bones' into the characters or things that you model to make it easier for you to animate them. Instead of moving all the points on, let's say, an arm, you could just move and rotate the 'bone' and all the points will move with it. There are also animation and rendering features. Rendering basically creates a picture of a view of your model that you want, which you can add lighting and color to right in the program. The animation part is basically a bunch of renders played back to back to create movement, but there are also the options to create your animation in a video format. There are also some much more complicated features like particle systems and a Realtime/3d Game Creator built in to the program. The particle systems can be used in creating hair, fire, snow, and other small random things. The built-in game creator isn't the greatest, but it looks like it can make some pretty decent looking stuff.
You can view some of the models people have created too by clicking HERE.
Windows 98, ME, 2000, XP or Vista
Mac OS X 10.2 and later
Linux 2.2.5 i386
Linux 2.3.2 PPC
FreeBSD 6.2 i386
Irix 6.5 mips3
Solaris 2.8 sparc
It does have a few minimum requirements and they are:
300 MHz CPU
128 MB Ram
20 MB free hard disk Space
1024 x 768 px Display with 16 bit color
3 Button Mouse
Open GL Graphics Card with 16 MB Ram
First it can be difficult to start out because there are many different commands to it.
It also doesn't come with any form of a tutorial, but now that it has been out for awhile some people have created their own tutorials. Click here for one of the better tutorials.
For those of you who may be interested . . .
Here are some of my own examples, this shows you what you can do (And these are only simple works)