On the list of guest operating systems at https://www.virtualbox.org/wiki/Guest_OSes
there are a small number which are marked with a red square and the comment "Doesn't work". Near the bottom of the list is "Visopsys", which is marked in this way. Although it is hardly a major operating system, I feel I must correct this statement.
Visopsys works perfectly well in VirtualBox. There is just one small glitch, which is easy enough to deal with once you realise what it is.
Visopsys runs without problem from floppy disk (but with a limited collection of utilities and programs) or from CD-ROM (but read-only). To use it properly you have to install it to a hard disk, and that is where the glitch shows up. If you try to install it to a "virgin" hard disk, then the resultant system will not boot.
The problem is caused by the partition routine in Visopsys which does not write the Master Boot Record of the hard disk correctly. The solution is first to create a partition on the hard disk using something else. (I tried it by booting using the Windows 98 start-up floppy, and then using FDISK from there, but I would expect other "fdisks" to do the same.) Once this has been done, then you can install Visopsys on the partition, and it will work fine.
This isn't a VirtualBox issue at all. The same happens if you try to install Visopsys to a new hard disk on a physical machine. It is simply that no-one is ever likely to do that, so the problem doesn't often arise there. When using a VM you are far more likely to start with a truly blank disk.
The system is one individual's hobby project, so it is rather limited and there is not a lot you can do with it once it is installed. But none of the issues are anything to do with virtualisation. It really ought to be listed as "works without additions", while noting the above partitioning point.