Hello, you failed to mention whether it's for 2D or 3D. If you're looking for 3D then as the guys before me posted, try Blender, it's free and has a great tool set. There's also plenty of tutorials to get you started. For 2D, if you want to go the frame by frame route for free then try Pencil, or you could pick up a trial version of Anime Studio Pro for cut out style 2D animation. For more advanced 2D animation you can also get trials of Toon Boom Animate and Animate Pro from ToonBoom. Hope this helps.