Aether is a tool which supports externally baking lightmaps within 3D software like 3ds Max rather than with the HEK's radiosity process. This allows for much higher resolution lightmaps than possible with Tool or Sapien, and shorter baking times since external software is much better optimized for lighting.
In order to externally light a BSP, all information about shadow-casting surfaces must be present. Aether supports extracting the BSP itself (crucially including its lightmap UVs), bitmaps with transparency, and instanced shadow-casting fixed objects like scenery.
The extracted assets can then be exported for 3ds Max or Maya using Aether's interactive GUI. Though Aether does not support Blender, it should be possible to transfer assets using a 3D interchange format like collada if the supported software is also available.
Within the 3D software, the artist can place lights and bake lighting to a texture using the BSP's lightmap UVs. Aether can then compile the texture back to bitmap format and optionally dither the texture to avoid banding, since lightmaps are 16-bit.