xtranormal is an amazingly easy tool to pick up and start using to create fairly detailed animated movies. They advertise the tool by saying "if you can type, you can make movies" and it really is that simple yet the range of options is quite extensive. You can pick your own characters, setting, camera angles, emotions, hand gestures and voices. Then, whatever you type in for a script the characters you select will say, so you can make your movies as complex or as simple as you want. I've included a sample below that is an interesting lesson on the letter B. While this particular example may not be the best representation of how you could use this with k-12 students, I think this tool has a lot of potential as far as a creative way for students to express their understanding of different concepts and subjects. As with many other Web 2.0 tools you can share your creations by giving people the URL or embedding it.