Many times it is necessary to integrate data and give remote users a shared access. But how to implement a secure solution that allows all users to have a repository on the server or some kind of cloud that works locally?
For situations like this you can actually use WebDAV that comes with IIS. It will allow you to mount an internal network share using a virtual directory. Users can map a drive right over the internet using net use f: https://server.fqdn/Virtual-Directory-name. I would only recommend this method if using 2012 server or higher, and having a valid SSL cert.
If you are comfortable with Linux you could try implementing Open stack. It is a free cloud framework which allows great expansion and security. There is also a big community so if you ever run into trouble it won’t be difficult to get help.
OwnCloud is also free, open-source and easy to implement solution. It can be easily integrated with LDAP and has mobile client. You also have the ability to set multiple profiles, and even integrate with some of the other cloud storage solutions.
Another popular solution good and free, is tonido. This one have mobile clients, 3rd party apps support and even camera uploads.
Regardless of the solution chosen, always have a backup regularly done.