> How does the business plan deal with the chance that it's perfectly in my hands (read: on anyone with whatever motivation, usually commercial) to grab the code and provide the same thing but cheaper or even free?
Here, it is just some extensions that are in a repository that is enabled by default in the main product (which is free and open source). Someone forking would not have their repository enabled by default. They could of course distribute their own version of XWiki itself with their repository enabled by default.
The extensions we sell also come with some basic support, so there's also that. At some point, if someone forks and sells for cheaper, they'll also need to provide the fixes and the features asked by their customers, at which point they'll not be able to keep up with cheap prices.
I suspect a former colleague who now works as a freelance might be distributing some of these apps to their customers (they contribute some fixes from time to time through pull requests).
I guess if it happens more largely we'd figure something out. Now, it's also not our main income. You might be right that it's niche enough to fly under the radar. Forking and maintaining a cheaper copy might also not be lucrative enough: the apps we sell answer needs of existing customers anyway, so we need to write this code anyway, but someone external would probably find something more lucrative to do with their time. I don't know :-)
Another good example I didn't think about in my first comment is WordPress extensions with their premium plans. Because of the WordPress license, you are forced to distribute your WordPress extension as open source. And this is probably less niche, for the biggest extensions.