I need a DECENT, FREE 2D animation software! Help please! (For Windows)?

I am trying to make a nice 2D animation but movie maker just wont cut it. Also, I'm sick of people bringing me to Adobe Flash or Free trial sites. I just want something simple like Flipbook or even Harmony. Could you please tell me about some nice software like that? PLEEEEEEEASE HELP!!! Please note it's gotta be FREE and DECENT.