Among ODB++ and IPC-2581 GenCAD is one of the most important file formats for PCBs. The primary focus of the GenCAD standard rests on fabrication and testing. GenCAD contains all information about a PCB ranging from net, component and route information, to complete layer setups in a single file which provides additional protection from data loss.

In some software you have export options, for a good result (e.g. for bottom side components) use e.g. this setting in target software:
How to set GenCad output options in target to get valid file for PCB-Investigator
(angle counter clockwise and no flip option)