Unless you want to spend a lot of money, it seems like your options for animation software consists of Procreate Dreams, or Blender. I find it a little weird that Procreate Dreams can create functional animation software for $20 on the Ipad, but no one else can seem to come close on the PC; too small of a market for anyone to care?
Using grease pencil is a little quirky, but I think once I figure out the quirks it should be a pretty good 2d animation software, and it's free; thanks Blender Foundation.