It seems OpenSCAD is capable of importing of both ASCII and binary STL files. As such, this is probable the most convenient and likely also only choice for making stl to scad conversion work. We do not know about any other 3rd party software that could perform this conversion.
Convert Stereolithography CAD file to OpenSCAD CAD model.
We found one software available in the database for this conversion.
Multiplatform software - convert stl to scad on any platform
A software for making solid 3D CAD objects
Convert from stl file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.