AS I already said, it's a level editor,
it can add and edit static meshs,
entities, terrain, physics, lights.

Nearly everything WED can do, too.
After you've finished you level, you can save it as WMB or you can build it directly.

Terrain editing isn't in development, but perhaps I will add this in an update, if the main program is finished.

Editing entites isn't in development, too.

But as I said in an other thread, the program is finished next year,I'll give you screenshots as fast as I can, I think next month.