I created some short films that you can load with the load animation menu. You can also create your own animations and save them on your browser local storage.
To add a keyframe double click on the keyframe line, you'll see a new red box.
You can select a keyframe by clicking on it, the box will change to red. Then modify the fields on the right to change the character in the current frame or press 'delete frame' to delete it.
You need to stop the animation to add/remove/modify keyframes or to select another animation
Pro Tip: use ENTER to jump to next section, and TAB to jump to next field. If you are in chrome you can use the up/down arrow keys to increase/decrease the value of the field.
This page works better in Chrome for Mac
The character used in this page is from the Spanish pre-school animated television series Pocoyo.