Open source software is so plentiful today that it's rarely news when a company decides to open-source code. It's more interesting when the opposite happens and a previously open source product becomes closed-source. That's what occurred this week at RoboVM.

RoboVM provides developer tools for building Java-based mobile apps. Previously, the company licensed its compiler under the GNU General Public License, or GPL, one of the most common open source licenses.

On Oct. 29, a RoboVM representative informed community members that the company will no longer make its code available under the GPL.

He explained that the RoboVM business model had previously centered on releasing an open source product "with proprietary extensions (like our debugger and interface builder integration)." Now, however, "in light of the low contributions and behavior of competitors, we decided to stop automatically releasing changes to the core of RoboVM as open source," the statement said.

The company emphasized that open source software "is close to our hearts," and apologized for failing to be more upfront about its decision to close-source its compiler until users began complaining about it in a community forum. But the bottom line remains clear: For RoboVM, open source proved ineffective as a way to make money.

So far, the company has not offered details about exactly what went wrong with its open source model. It has only made general statements about how its open code failed to attract many contributions and apparently made life easier for the company's competitors.

It's also unclear to what extent RoboVM's recent acquisition by Xamarin may have played a role in the decision to close-source the compiler. But we're betting the timing was more than a coincidence.