From the 'Old Open Source Business Models Reborn' files:

The term open core is poison for an open source project today isn't it?

More often than not, the term open core refers to some crippled piece of open source software that only really works when paired with some type of proprietary shell that make the software usable.

Yet, the open core model – is still what many open source software firms (or at least, those that have raised venture funds) are embracing.

There is another way.

It's called the Layered Open Source Model, which is kind of like open core, but not nearly as evil. The first person I ever heard use the term (and likely the one who should get credit for 'coining' it is Emil Eifrem, the co-founder of the Neo4j open source NoSQL project.

Traditional open core is where the core project is open source and the add-ons are proprietary and commercial. For Neo, that's not the case. Their advanced and enterprise software editions are still open source, but under the AGPL.

"The AGPL basically says that if you're open source, than I'm open source. If want to contribute to the commons, awesome, you can use my AGPL software for free," Eifrem told me. "But if you want to take it off the commons and you want to make money, than we should make money too."

Layered open source is a variant to open core the difference is that all the software that Neo sells is still available under an open source license.

"I've never liked open core not because it's immoral or Richard Stallman hates it, I never like it because it's not a clear method," Eifrem said.

The trouble for an open core vendor is that on one hand they're telling customers that open source is great and produces superior software. On the hand the open core vendors are saying open source is great, except when it comes to the stuff they want to charge for, which will be kept secret. It leads confusion since if open source is a superior model, shouldn't it superior for the add-ons too?

Yes, I know, this does sound a bit like the dual-licensing strategy that MySQL pioneered. Just like open core now, dual-licensing also isn't loved by all today either, as people still worry that some the commercially licensed elements are somehow different than the open source ones.

I don't know if Eifrem's Layered Open Source model will ever take hold, there is too much money in open core already. That said, Red Hat is a Billion dollar company on (mostly) open source, so why can't some other (mostly) open source model work too?

Sean Michael Kerner is a senior editor at InternetNews.com, the news service of Internet.com, the network for technology professionals. Follow him on Twitter @TechJournalist