Best free 2d animation software? Thread

I need a free 2-D animation software for windows that I can use to make video game trailer. I also need to be able to edit individual pixels. Please recommend your favorite with if it matches criteria. Thank you.

For sprite based, frame by frame, animation? I would suggest Graphics Gale, it's pretty solid. Spine is also a really good skeletal animation tool. Some artists just do the frame by frame and onion skins in Photoshop or GIMP using layers.

Thanks. I will try those out!