Epic Pen allows you to draw directly onto your screen, making it perfect for leaving drawovers, notes and visual feedback on animations
Epic Pen
Animation Mentor
Animation Mentor is an online animation school. The original online animation school taught by professional animators to grow you in the art of character animation.
iAnimate
iAnimate is an online animation school. They offer a complete set of workshops designed to target all animation needs, and put you in direct contact with veteran animators from the biggest & best studios in our industry.
Kinovea (FREE)
Kinovea is video player that allows you to slow down, study, draw and comment. Primarily made for sports enthusiasts but useful for animators too.
Syncsketch
Syncsketch is a really useful free website for posting work and receiving feedback. Just upload a video and allow others to review, draw and make notes.
Animator's Resource Kit 