The Animation Paper – Pre Release is now available. Currently in Alpha but check it out, download it and give feedback
Advanced Skeleton has been used to rig creatures, props, vehicles and just about anything since 1999. It is free to download but if you want to use it for a commercial project you will have to buy a license.
The Setup Machine
The Setup Machine enables Maya users to easily and quickly rig a wide variety of CG characters with just a few clicks. Generate a flexible, modern character rig in minutes saving you days or weeks of work
Grease Pencil is a feature inside Blender that allows you to animate in 2D while taking advantage of a full 3D suite of features. Definitely one of the best pieces of software that blends the two together so seamlessly (and free!)
Storyboarder is a free open-source piece of storyboarding software that makes it easy to visualize a story as fast you can draw stick figures.
Akeytsu is a piece of 3D animation software and is a lighter, faster and cheaper alternative to Maya. It also has a free educational version.
Live2D has a bunch of software that allows 2D artists to create animations from their artwork. Available in both FREE and PRO versions.
Dragonframe is the stop motion animation software that captured Laika’s ParaNorman, The BoxTrolls and Disney’s Frankenweenie. Free Trial available.