I think synfig’s strong suite is in being able to animate without doing it frame-by-frame, so I’d like to suggests features found in crazytalk animator, because it’s the closest thing to synfig, but where synfig would win is that it has drawing features.
if another kickstarter project comes, please consider including these into the feature list.
It involves being able to save your animations to the library and apply it to other drawings you’ve made.
For complex animations, they use a sort of template bone system for body and face, any characters you’ve made that is classified under the specific bone system can share the same animations.
Here are some of their cool features: