BlueBrick, by Alban Nanty, is a software for designing LEGO Train layouts. It has an LDraw input and output mode, and can produce either .ldr or .mpd files. But since BlueBrick does not directly use the LDraw parts library, when reading a LDRAW file, BlueBrick may display unrecognized parts with a default "missing part" red cross image.
BlueBrick also can read and create Track Designer files, and requires Dot Net 2.X to run on MS Windows, or Mono to run under Linux or Mac.
BlueBrick uses a layers paradigm, where elements can be placed on various layers, and layers made visible or invisible. There are four different types of layers: Grid, Brick, Area Assignment and Annotation. Brick layers is actually a generic part layer that can contains table, baseplates, road or train tracks. Thus, one can do tables on a table layer, lay down roads and baseplates on a baseplate layer, and so forth. Layers can be reordered, and made visible or hidden as needed. Any layer can be made translucent using a slider scale, which is quite convenient for the area layers.
Track and roads feature connection points to allow for easy alignment and there is an adjustable snap-to grid.