Every structure permissible by physical law
It is often thought that APM is supposed to be able to produce almost anything (often formulated: all allowed structures permissible by physical law) including e.g. food, wood, plastics and metal parts but this is surely not the case.
The range of materials and structures targeted actually lies in a very narrow range (see: "mechanosynthesis"-page). The magic lies in the diamondoid metamaterials that emulate properties above the atomic level.
This is not to say it will be impossible for all times to assemble materials (or rather compounds) lying outside the narrow set of now targeted materials. When the technology will have been around for quite a while very advanced extensions may be able to do this but this is way beyond the scope of any current day APM attainment project because it is beyond the horizon of useful exploratory engineering.