If you are looking for 3D flash engine you have multiple open source choices. The best one offers modeling editors, so creating your scenes is click easy, or other animation / physics frameworks, pixel bender shaders etc. List of most popular 3d engines:
Papervision 3D, is most common and widely used 3d engine. You can edit your models and scenes with VizualPV3D.
VizualPV3D is a Flash Visualization Application that provides a GUI interface to create and manipulate objects in 3D scenes using Papervision3D. (VizualPV3D)
Away 3D, looks like the most advanced engine on the market now. Is based on Papervision. In Flash Player 10 it uses Pixel Bender for better performance. It offers super advanced tool to create your scenes in away3D – PreFab3D (AIR application). See demo video
PreFab3D application is an attempt to simplify common tasks, improve the workflow and greatly enhance the visual quality of your Flash 3D productions. It’s a small but powerfull tool that can add visual quality to low polygon models using a nice bag of tricks thanks to the advanced rendering capabilities of Away3D. (PreFab3D)
- Demos and examples, usign Pixel Bender
- Manual / documentation
- Scene / model editor
Sandy 3D is a Flash 3D engine, available in 3 versions: AS2, AS3 and haXe. Interesting thing about this one is, there is and 3D physics engine called WOW-Engine.