Dropbox has had a horde of programmers working on this for many years and nothing seems close in the personal NAS area. Either it's too hard for folk to setup or as you found out, requires sharing details you don't want to share.
The drive is just your raw storage so for the Dropbox clone system you speak of you need a host system to run it.
Next month I'm going to try this: https://www.google.com/search?q=raspberry+pi+nas+dropbox+clone
I currently use Dropbox which I set up so my sister, brother-in-law and parents can all add to the account for viewing pictures and videos of family. Works great, but size is obviously a limitation. Setting up my own personal storage is something I always wanted to do so this gives me the motivation to do so.
I have an older 1TB WD external hard drive which I have plugged into the back of my Asus RT-N66U router and set up iacloud. I am able to get it working just fine... for me. In order to let others in I have to give them my router login info. Family or otherwise -- not happening. Plus the interface is not friendly enough for them.
Now aicloud does allow you to share files by generating a link from a file that I can share via text, email, etc., but it doesn't work, and I need to share an entire folder which aicloud appears to not offer. The router does have the capability to limit who can view what folders in the router settings, but it appears to only work for users connected to my network which no one is or will be.
I am hoping to avoid purchasing a dedicated NAS since I still have a perfectly working external hard drive. I know my current drive is only USB 2.0 (as is the router), but testing it by streaming a movie from outside my network using aicloud seems to work just fine, albeit a tad slower for the initial load, but manageable.
Is there a way I can use my current external drive to run like a true NAS and work similar to Dropbox? One where I can block access to all folders except the one folder I would initially set up for the family so they can view/read/write as needed? Perhaps using something like Bittorent Sync or something similar? And I should mention it needs to have an app as my family views everything from their phone (and it needs to be as screw up proof for them as possible).

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