To update the terminology - the RedHat model is freemium - you give away something to market the part that you sell.
The problem with freemium is always how much you give away and how much you charge for. One idea that I have not yet seen is to do the split in the time dimention - sell licenses that convert into a Free Software or Open Source license after a year or two.
Sure, I work for Red Hat. You pay for support, training, access to consultants, certifications. All software is available for free, just with trademarks removed.
> Just to be clear so you say that there is nothing non-GPL in the software that is bought there?
Correct. There are trademarked components (graphics, etc.) that cannot be redistributed but they are not software. The same is true for Mozilla Firefox, for example, even though it's both gratis ("free beer") and libre ("free speech").
There are also a few "supplementary" packages that are non-free but it's stuff like Oracle JDK or Adobe Reader. It's more akin to Debian nonfree than to an open-core model.
> Self-support (1 year)' contract - this sounds like there is no support, training or access to consultants being bought there.
Correct, in that case you only pay for certifications, knowledge base (which is also part of support) and access to the updates.
The problem with freemium is always how much you give away and how much you charge for. One idea that I have not yet seen is to do the split in the time dimention - sell licenses that convert into a Free Software or Open Source license after a year or two.