A lot has been written recently about so called “Open Core” software ever since Andrew Lampitt coined the term back in August of 2008. Many analysts have been critical about it, such as Richard Hillesley from The H Open in his recent article “Open core, closed heart?”. Many are also very positive about it such as Matt Aslett from The 451 Group. However, I think that most them are missing the elephant in the room: Open core is not sustainable in the long term because it represents the worst of both worlds. Open core tries to find a middle ground between proprietary software and free software, but it reaps the benefits of neither and inherits the problems of both.Let me show you by example. SugarCRM is one of the more popular open core software products available. The company offers the Community Edition for free under a GPLv3 license but also offers a Professional and Enterprise edition under a proprietary license. SugarCRM has been around since 2004 but it is already showing many signs of not being sustainable.