tween 是一个 js 动画引擎，也被 Unity3D 使用。
在 Bitbucket 上的地址 https://bitbucket.org/orx/orx
The iio Engine was created to streamline the process of developing HTML5 applications.The ownership of the iio Engine rests in the hands of the open source community. Contributions to the core library and additions to its collection of extension packages are always welcome. New branches and merges are managed through Github.
The iio framework was designed by Sebastian Bierman-Lytle of Denver, Colorado, and he continues to maintain and advance the Engine while pursuing a Computer Science degree at Dartmouth College.
Unity 插件，售价 $30.
Blender 2D animation