Tweening classes for Flash makes it easier & more stable to create animations based on real time rather than Flash frames.

Tweener is a class used to create tweenings and other transitions via ActionScript code for Flash.

The fluid syntax of Tweener allows it to be used to tween any numeric property of any object of any class, so it is not tied to specific properties of built-in classes such as MovieClips or TextFields.

Once included on SWF movies, Tweener currently takes 8.8kb (AS2 FL2), 9.2kb (AS2) or 10.4kb (AS3) of the total compiled file size. It can be compiled with the Flash IDE, MTASC, or Flex SDK (even with strict rules on).

It’s released and maintained for these versions:

• ActionScript 2.0, for Flash 7+ and Flash Lite 2.0+
• ActionScript 2.0, for Flash 8+
• ActionSctipt 3.0, for Flash 9+

Flash tweening animations can be done easier & with less coding using Movie Clip Tweening Prototypes.

Most features of Movie Clip Tweening Prototypes are from Fuse, which is a powerful Flash animation toolset.

There are also free .fla files of  very nice examples built with the prototype.

Note: This is an ActionScript 2 prototype.

A benchmark test of Movie Clip Tweening Prototypes & some other famous classes can be found here.