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.
FlipaClip
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
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
Akeytsu
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
Live2D has a bunch of software that allows 2D artists to create animations from their artwork. Available in both FREE and PRO versions.
Dragonframe
Dragonframe is the stop motion animation software that captured Laika’s ParaNorman, The BoxTrolls and Disney’s Frankenweenie. Free Trial available.
After Effects
After Effects is an adobe product and is a very popular motion graphics and visual effects programs. Useful for editing and adding post-effects to animations.
ToonBoom
Toon Boom Animation is the leading supplier of animation software and storyboard software for animation studios and media publishers.
Animator's Resource Kit 