Allow applications downloaded from anywhere in macOS Sierra In previous versions of the OS in the security pane, you are provided an option of:



But in this version there is no option anywhere:



Is there a way that I can turn on anywhere? (via Terminal maybe?)
Apple have removed this function on macOS Sierra, but you can re-enable it running this in terminal:
sudo spctl --master-disable 


Additionally, as Jack points out:

Granted this is a little overkill, but it does the job reliably. It can be re-enabled immediately after launching the application with
sudo spctl --master-enable