Animation Programs like Adobe Flash are very expensive, but Pencil is a free Open Source animation program written by animators for animators. And, Pencil also has the best user interface for creating hand-drawn animation. Pencil is compatible with Mac, Windows, and Linux. Shown below is a short example of what Pencil can do:
Pencil is a 2D animation program designed to automate traditional cartoon style animation. In traditional cartoon style animation, artists use a flipbook to test their animation. In pencil you also create pages which you can flip, you can flip back and forth between multiple pages, or you can set the page flipping speed (frames per second) and set the animation to loop.
Pencil has an "onion skin" feature which lets you see through a page to make that tiny change in each frame needed to create the animation movement. It also has a "size with pressure feature" which defines the brush stroke with the amount of pressure applied.
When your animation is complete you can export your image sequence and color palette, and you can export the animation as either a Quicktime Movie or a Flash Movie (.swf).
The Pencil website has a user forum where you can ask questions, learn how to use the program, and get in on discussions on what users are doing with Pencil. There is also an extensive and well illustrated User Manual.
The Pencil download page is here. Make sure you download the appropriate version for your operating system.
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