From a completed kickstarter by Real Game FX:
The first machine is the "Fog Monster" which uses a pipe system to deliver the fog into your game. This design allows you to hide the pipe behind your existing terrain pieces so that the fog enters like it is part of the natural environment.
The second Fog Machine is the The "Dark Crypt" Fog Machine. The Dark Crypt is meant to be placed in the game terrain and produces fog that exits through the doors and windows.