I was surprised to learn that Paragon Software released a free APFS to HFS+ Converter app.  As the name would indicate, this app claims to be able to take a drive formatted as APFS and convert it to HFS+.  This is an interesting tool, and could be helpful to those who upgraded to High Sierra, had their SSD boot drive automatically converted to APFS, and this has caused some sort of problem (like not being able to host network Time Machine backups).  I’m betting this tool will only be useful for macOS 10.13, as it would appear Mojave will require APFS, but it’s worth knowing about none the less.