Adds factory buildings you can walk into and build parts of your factory inside. This mod will not be updated for Factorio 0.15! Get Factorissimo2 instead, it's much better.
As a note to MagmaMcFry
It seems many people are under the misconception that the west side is input and east side is output. (they usually seam to miss the north sides IO entirely)
Might be time for an FAQ? ;)