Website / API to manage files/roms on a retropie install. This application can then be hosted on a windows/linux server separate from the retropie.

If using a windows server then follow instructions here. From the instructions I found that I needed to add a password

sudo mount -t cifs -o username=domainusername,password=yourpassword //ip_add/ShareFolder /media/BACKUP

I couldn't get the smb credentials working properly so I added this in the fstab file.

//ip_add/ShareFolder /media/BACKUP/ cifs username=domainusername,password=yourpassword,iocharset=utf8,sec=ntlm 0 0

The following package might need to be installed to get the windows file share working properly.

sudo apt-get install cifs-utils

Windows firewall rule might also be needed (for traffic between windows server and retropie).