I used an older version of Moho to animate the characters in the first AdventureX Kickstarter. Nothing terribly impressive, but I was just trying to get to grips with the software: https://www.kickstarter.com/projects/adventurex/adventurex-2016-the-narrative-games-convention
I encountered a few glitches with the old version. But it was pretty good, overall, and all about skeletal animation. There's also Adobe Animator. And I know everyone thinks Blender is very complicated (because it is). But it's free and much less unfriendly than it used to be, and I use it all the time for 2D animation. You can do traditional frame-by-frame drawing or rig the characters with a skeleton:
https://www.youtube.com/watch?v=iTNIVvuNeCQ&list=PL0MITQcQ2hJaz7uNiZ2T1uHKs2gl6K6gD
I encountered a few glitches with the old version. But it was pretty good, overall, and all about skeletal animation. There's also Adobe Animator. And I know everyone thinks Blender is very complicated (because it is). But it's free and much less unfriendly than it used to be, and I use it all the time for 2D animation. You can do traditional frame-by-frame drawing or rig the characters with a skeleton:
https://www.youtube.com/watch?v=iTNIVvuNeCQ&list=PL0MITQcQ2hJaz7uNiZ2T1uHKs2gl6K6gD