BlueBrick, by Alban Nanty, is software for designing LEGO Train layouts. It has an LDraw output mode, and can produce either .dat or .mpd files. It also can read (but not write) TrackDesigner files. It runs on MS Windows systems and requires .net 2.0
It uses a layers paradigm, where elements can be placed on various layers, and layers made visible or invisible. There are multiple types of layers, Grid, Table, Baseplates, Track, Assignment, and annotation. 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.
Track and roads feature connection points to allow for easy alignment and there is an adjustable snap-to grid.