Shareware? That was popular in the 1990s, but also not sustainable as a licensing model.
Never said it was sustainable.
Also, better not include any Open Source projects in your Shareware product, that's as illegal as the people who will delleberately (and accedentally) pirate yours.
Actually, that depends on the license. MIT License, BSD-3, and many others don't have any rules against commercial use of their code. Some require attribution, others don't. So long as you're respecting the license terms, you can absolutely use Open Source code in your shareware product.
Using code licensed under the GPL (or, in some cases, the LGPL) in your shareware product, that's another topic entirely.
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Never said it was sustainable.
Actually, that depends on the license. MIT License, BSD-3, and many others don't have any rules against commercial use of their code. Some require attribution, others don't. So long as you're respecting the license terms, you can absolutely use Open Source code in your shareware product.
Using code licensed under the GPL (or, in some cases, the LGPL) in your shareware product, that's another topic entirely.