Build.exe is a first-person shooter engine created by Ken Silverman for 3D Realms. This editor was the original editor of the game used for creating levels in .map format. This editor has since been expanded upon and replaced with Mapster32 thanks to the hardworking team over at Duke4.net who have also made the new editor compatible with today’s latest operating systems.
The developers at Duke4.net have been very careful in maintaining backwards compatibility with the older Build.exe format as well as offering better program stability, functionality & enhancements such as: a new V9 map format for supporting TROR or True Room Over Room and several different graphical renders to choose from including: Classic Mode \ Polymost & Polymer. Hopefully, an optimized Polymer renderer will be available along with multi-player support, which we have all been patiently waiting for.
For more information about the innards of Mapster32 please take a look at the Mapster tutorial section which is composed of fan based tutorials and example maps to assist with creating your own design.