I want to install on my macbook pro a second osx sierra. I prefer to use virtualbox for this second osx. The reason is that i will try to install composers, virtual hosts lavarel etc. and i dont want to harm my main osx.
I just followed these instructions, and they seem to have worked: sierra-virtualbox-install.md.
You'll need the Install macOS Sierra.app from Apple, and you'll need to change the first step of the instructions to match it's name (remove "\ Public\ Beta"). I also had to format the virtual disk manually after booting with the install image.