Synfig eliminates the task of manual tweening, producing smooth, fluid motion without the animator having to draw out each frame individually. This allows you to produce 2D animation with fewer people while producing art of a higher quality.
Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline-modeling, rigging, animation, simulation, rendering, compositing and motion tracking, video editing and 2D animation pipeline.