And as a personal user, I can't use any code from Duplicacy in any other project. I can't even, say, create a package for it and get it included in Debian.
And aside from some of these practical issues, I'm a personal user who supports software freedom so I don't want to use something encumbered in this way.
And as a commercial user, any development contributions I make are no longer my own and I have to pay to make use of them.
But the worst part of it is, your license isn't very well defined. As it stands, you may at any point stop accepting license payments from a commercial user and they'd lose the right to use it entirely - they'd lose access to their backups (unless they used the software without a license).
You of course have the right to choose any license you like! I just wouldn't use duplicacy myself under the terms of that license.
The AGPL license might be a step in the right direction (for your requirements). It aims to at least ensure that if companies use the code to provide a service to other users, they have to release their changes. You can sell those companies a different license if they don't want to accept the AGPL (you'd have to have a contributor agreement to assign copyright to you though, to allow you to relicense code at your discretion like that).
Or there is the open core model (like nginx-plus), where you provide the code under an open source license but provide some additional "enterprise" features (like your vmware stuff) to only those that pay. I'm not a fan but it seems to work for some.
Anyway, duplicacy sounds a great design. All the best with it!
From a practical standpoint, it makes it more difficult for me to trust that it will be maintained in the long-term, or that I can extend its functionality if I see a need.
Ideologically, I'm somewhat uncomfortable using duplicacy when fully-free alternatives exist. I'm not a free software purist by any definition (I use steam. I have a Netflix subscription. My android has google apps on it.), but this is an area where compelling free software solutions do exist.
The license also keeps it from being packaged in most Linux distributions, which makes it a nuisance.
Duplicacy sounds great but it has 6 [0] contributors and Borg has 107 [1]. It's obvious which one has more eyes on it.
Plus I can apt-get install borgbackup / apt-get upgrade which adds another level of trust.
If this were BSL licensed, the community could fork it if that became an issue:
http://monty-says.blogspot.com/2016/08/applying-business-sou...
I'm curious to see whether any BSL software manages to build a third party dev community (inclusion in debian non-free, third party patches and bug reports, etc)
While I have your attention: It'd be great to measure how many bytes the solutions read and write, as well as I/O counts. There are tools for this in Linux, and probably MacOS. Alternatively, network bandwidth would be a good proxy for these measurements.
