Not free, but new: LightWave CORE

Newtek, developer of the popular LightWave 3D modeling, rendering and animation software, will soon release its next generation engine: LightWave CORE.

http://www.newtek.com/core

It will be more expensive (+/- $1500) than current LightWave (+/- $800), with higher subscription pricing (+/- 500), but more open for customization: CSS-based user interface, same Software Developers Kit as internal Newtek team and cross-platform: Windows, OSX and Linux, in 32 and 64-bit.

It uses Qt for the GUI, Python for scripting, C++ for development and Collada as file format (extended, I assume).

It looks like a mixture of modern development, but still in the context of traditional desktop applications, which seems appropriate for animation software.