Epic Pen allows you to draw directly onto your screen, making it perfect for leaving drawovers, notes and visual feedback on animations
Animation Paper – Pre Release
The Animation Paper – Pre Release is now available. Currently in Alpha but check it out, download it and give feedback
MocapX
MocapX is a Facial motion capture app for the iPhone that streams the mocap data to Maya in real-time
FlipaClip
FlipaClip is an animation app for android and iOS that has a simple UI. Free and Paid versions can be downloaded from the Play Store and App Store.
Advanced Skeleton
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
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!)
Rough Animator
Rough Animator is a fully featured hand drawn animation application that runs on Android, iOS, Mac OS, and Windows. Currently available for $4.99