What is Synfig? It's website defines it as "a powerful, industrial-strength vector-based 2D Animation software package, designed from the ground-up for producing feature-film quality 2D animation with fewer people and resources."
I must confess that I do not do animation but I do love watching animated movies. :) There are popular commercial software that costs thousands of dollars per seat but I was pretty amazed by the quality of the output from this open source application, Synfig.
If you are an avid animator, I definitely recommend that you check this out before you spend your hard earned money on expensive commercial software.
(image from Synfig website, apologies)