The software is released under an open source license, but has a single entity with full control of the software’s copyright.
Dual Licensing is a model where the software is released under an open source license, almost always a copyleft license, but has a single entity with full control of the software’s copyright. This enables the company to re-license the software as they see fit - either to sell it under a non-copyleft license, to run it as a service, or to sell proprietary versions, while restricting the rights of others to do the same.
Who Uses it?
When should it be used?
A tool used primarily by venture backed startups, with a single company in control of the asset. The goal here is that the software is useful to a wide market with the copyleft terms attached, but for certain segments of the market, or to create your own proprietary derivative, you retain the rights to remove the copyleft.
What kind of monetization is possible?
Depending on the type of copyleft license, it ranges from simply selling identical software without copyleft terms (for embedding, as an example), to being allowed to run the software as a service, to being allowed to build fully proprietary distributions with enhanced functionality.
In any case, it is used to create a functional monopoly on monetization for the company.
Does this model help create a Sustainable Free and Open Source Community?
No. It trades the fundamental liberties in the core commitment in exchange for revenue.