Is the enthusiasm for open source software projects a "bubble" ready to burst and take the model down with it? That's what the CEO of one of the most successful open source projects thinks, even while a new crop of software--his included--is taking its place among the most established.

"Right now, open source is hot," says Rod Johnson, author of the Spring Java development framework and CEO of Interface21, the company he founded to market it. Most open source projects are supported by an army of volunteers who buy into the hype, but "capitalism will inevitably reassert itself" and developers will find they need to put more effort into steady jobs and private lives, leaving "open source zombies"--unsupported, unmaintained projects--he predicts.

Also, venture capital will get over its romance with open source soon enough and move on to other hot options, he foresees. In the last 12 months, $160 million has flowed into fledgling open source companies, Johnson says, but unless they make quick returns, bye-bye VCs. "Venture capital is cyclical. It invests a ton of money in a segment, then it disappears," he says.

Instead, open source products "should be funded by their customers," the only way to ensure they that have a future, Johnson says. It's no accident that the best known enterprise open source programs, such as the MySQL database and the JBoss application server, have companies with paying customers behind them. Furthermore, core development is no longer a matter of volunteerism: Key developers have been hired by MySQL AB or JBoss Inc., now a unit of Red Hat.

NO ZOMBIFICATION HERE

Spring isn't in danger of zombification. In response to an increasing flow of support revenue from Spring's 1,000 users, Interface21 has gone from seven employees two years ago to 35 today. The company employs many of the key Spring developers.

Spring isn't the only one. JasperSoft, an open source business intelligence app, has more than 5,000 commercial customers. There have been 2 million JasperSoft downloads, half occurring in the last year. There are 30,000 developers registered on JasperForge, its open source project site, with 130 projects under way, eight sponsored by JasperSoft Corp., the company behind the product. QED Financial Systems in Chicago has built JasperSoft's BI tool into its core trading system, and Salesforce.com and the SugarCRM and CentricCRM open source applications use it as well.

Hyperic HQ is open source system management software with more than 250 paying customers. John Shin, director of systems at MyNewPlace.com, installed Hyperic last year to monitor and help manage a mix of open source and commercial systems for his site, which registers 40,000 apartment shoppers a day in cities across the United States. Hyperic was easier to install and experiment with than IBM's Tivoli or HP's OpenView, he says, at one-third the cost of OpenView.

Mule is an enterprise service bus that's gaining traction in financial services and retail installations. Mule is backed by MuleSource, a company formed by its core developers to sell technical support for the system. At a conference for Mule users in San Francisco late last month, Dan Cahoon, senior architect at H&R Block, said the tax preparer is using Mule to roll out a virtual tax system that captures clients' tax documents and moves them around digitally to as many as 13,000 offices.

While the majority of open source projects will fade into obscurity, Hyperic, JasperSoft, Mule, and Spring appear to have the critical mass of customers, developers, and employees at financially viable companies to join the ranks of enterprise software.

This article was updated on April 16 to correctly identify QED Financial Systems