Pencil | open source animation and drawing software

Update:
@ibeardslee has pointed me to a forked, updated version of this software called Pencil2D, which appears to be a better option than the link I give below.
(Link)
"Pencil is an animation/drawing software for Mac OS X, Windows, and Linux. It lets you create traditional hand-drawn animation (cartoon) using both bitmap and vector graphics. Pencil is free and open source.

Pencil is not intended to mimick web-oriented vector-based animation software such as Flash. Its main purpose is to make traditional animation. Neither does it try to rival commercial software targetting the professional animation sector. Pencil is intended to be a simple programme enabling anyone to make 2D animation."
(Link)

Stop motion animation with Luciole

A couple of students came to me recently to explain that they needed help with (what appeared to be) a really complicated process for creating stop-motion animations. They were doing something in Photoshop with some proprietary plugin that could only run on a particular computer, and were unable to bring that computer to school. It got me thinking: the process of creating stop-motion animation is not complicated, so surely there must be some easy-to-use software out there for creating animations. The short answer is: there is.
I installed Luciole from the Ubuntu repository (took me 30 seconds to download and install) and it turned my laptop into Peter Jackson's studio. Thankfully it was wet last weekend, so I turned the kitchen table into a brickfilms stage. My first effort was far from interesting (my wife just frowned and shook her head when she saw it) but now I can't wait until my son is old enough to make films with. I'm sure, however, that in the tradition of train sets and meccano, the grown-up will have more fun than the child.
And if that isn't enough to encourage you to try it out, would break dancing plasticine men convince you?

I chose to be a bit less ambitious with my first attempt:

Yo Frankie!

One of the most high-powered, full-featured open source applications is Blender 3D. It's an incredibly powerful 3D modelling application that has been used to make short films like Big Buck Bunny and Elephant's Dream. So what do all those 3D characters do after their film careers end? They get jobs in computer gaming. Using all of the models and landscapes from Big Buck Bunny, the blender community has created Yo Frankie!, a 3D game with very impressive graphics, that is free for anyone to download and play.