K-3D features a robust, object-oriented plugin architecture, designed to scale to the needs of professional artists, and is designed from-the-ground-up to generate motion-picture-quality animation using RenderMan-compliant render engines. We strongly recommend the Aqsis render engine for use with K-3D.
The list of stable plugins you can find here: http://www.k-3d.org/wiki/Stable_Plugins
K-3D allows you to create and edit documents in multiple realtime OpenGL solid, shaded, texture-mapped views. You can even model, animate, and interact with animations while they play back for maximum productivity!