Synfig Studio (32-bit)

Synfig Studio is a free and open-source 2D animation software, designed as powerful industrial-strength solution for creating film-quality animation using a vector and bitmap artwork. It eliminates the need to create animation frame-by frame, allowing you to produce 2D animation of a higher quality with fewer people and resources. Synfig Studio is available for Windows, Linux and MacOS X.

Synfig Studio Features:

Layers
Synfig supports a multitude of layers of various types; geometric, gradients, filters, distortions, transformations, fractal and a few others.

Bones
Full-featured bone system allows to create cutout animation using bitmap images or control your vector artwork. The Skeleton Distortion layer allows to apply complex deformations to bitmap artwork.

Spatial resolution-independence
Most elements are vector-based, and all layers are parametrically generated, hence even when changing the target resolution of a project, the only pixelation will occur in imported raster images, not the built-in components.

Temporal resolution independence
Animation-keyframes are automatically interpolated by the computer, resulting in smooth motion

High Dynamic-Range Imaging (HDRI)
By using floating-point math in the image calculations, HDRI processing allows canvases to internally understand a far greater range of pixel luminance, resulting in better lighting effects, and improved color composition.

Sound support
Synfig have basic features for syncing your animation with soundtrack using Sound Layer. Linux users can get all benefits of full-featured audio editors through the JACK integration.

Pentablet-friendly tools
The draw tool can read the pressure sensitivity channel off your favorite tablets, for natural line weighting, and more to come!

Artist-oriented design
While it may not be obvious in this early state, Synfig (and its proprietary predecessors) has been designed from the ground up with animation workflow in mind.

Path-based Gradients
Unlike purely SVG-based vector software, and most consumer-level animation programs, Synfig has full support for gradient paths - gradients that follow along a drawn shape. This allows artists to easily add soft shading to animation without the trouble of painting it onto every frame.

Also Available: Download Synfig Studio for Mac