Free Level Creating Software?

I just wanted to know, are there are any free level-making programs out there? I have Blender, but I personally don't think that it's any better than Unity for making levels. (Great for models though...).

By level, what exactly do you mean?

If you mean terrain, Unity has a pretty good terrain engine (except it doesn't support concave shapes). Read more about the terrain engine in the manual.

If you mean level as in a 3D platformer, I'm afraid you cannot create that in Unity (unless you use really basic shapes like cubes, spheres, etc. - but I wouldn't recommend that). Blender would be fine for that.

If you mean level as in a 2D platformer, you also cannot do that in Unity, like above. Blender would also work fine.

The best free 3D modeling program that is fully compatible with Unity is Blender. There are a few others that are semi-compatible (you can export to Unity-compatible file formats), such as Milkshape 3D, but Blender would be the best.

Levels are essentially a collection of models so your best bet is to use Blender or Wings3d.

I don't think there are any BSP programs for Unity. Best to just model terrain in Blender as models/tiles and use that.