The primary goal of Smrender is to create high-quality charts suitable for print-out. Although it originally was intended to make sea charts, it can be used for any kind of maps as well.
The primary output format of Smrender is PNG which is a well-known raster image format. Unfortunately, many GIS applications cannot or at least not easy deal with it. The reason for this is that PNG basically does not contain any geographic information, such as reference points and the chart scale.
RNC (Raster Navigational Charts) is a pretty old (and weird 😉 format which was developed by the NOAA with the original intention to store digital marine raster charts. Today it is widely used by GIS applications, GPS devices, and smartphone applications. RNC files typically have the file extension .kap and are often also referred to as BSB files.
Smrender now is able to directly create such KAP files. It was implemented by using the documentation of libbsb and partial reuse of the code of it. To create a KAP file use the option -k.
Please have a look at the documentation of Smrender for further details.