Scene management is what a 3D engine internally uses to keep track of the world and the objects in the world.
A world editor is a tool with which one can make worlds for 3D engines. So it is not the same as scene management
but with a world editor you can define a scene for the engine.
To make worlds for Crystal Space there are four ways currently:
- Blender: Blender has a very good exporter for Crystal Space so this is probably the most powerful way to make Crystal Space worlds right now
- 3DsMax: Crystal Space also comes with an exporter for 3DsMax. The PlaneShift project uses this to make their worlds.
- CSEditor: CS has itself an editor included but it is in heavy development so not really useful right now
- AresEd: I'm working on a world/game building tool which is also in heavy development: more information: http://code.google.com/p/ares/
Let me know if you have more questions.