If you've ever seriously looked into character animation in Adobe After Effects, you've no doubt already heard of Duik, a free toolset that was specifically designed to aid in the creation of character rigs and character animation. People that use Duik seem to swear by it, and I've recently begun to experiment with it myself (sorry Moho! You just need to stop crashing on me!). What you may not know is that there is currently a crowdfunding campaign underway with the goal of funding the development of a new version of Duik, which apparently is to include a redesigned interface, a new feature called "Animation Blender" which looks similar to non-linear animation (!), and a ton of other new features. Take a look at the crowdfunding campaign, and pitch in if it looks like a useful tool to you!