Sun Microsystems' JRuby team is leaving the company to work for application hosting company Engine Yard, citing the uncertainty surrounding Sun's planned acquisition by Oracle.

Sun hired Charles Nutter and Thomas Enebo, often called "the JRuby Guys," about two-and-a-half years ago so they could work full time on JRuby, an implementation of the Ruby programming language for the Java Virtual Machine. Some months later Sun hired Nick Sieger, another key JRuby developer.

All three will start work at Engine Yard next week. Nutter said they decided to leave Sun largely because of the uncertainty resulting from its acquisition by Oracle, a deal that's expected to close later this summer pending regulatory approvals.

"To be honest, we had no evidence that Oracle wouldn't support JRuby, but we also didn't have any evidence that they would," Nutter said by telephone Monday. "Two out of the three developers making this move have families; we want to make sure JRuby will get to the next level, and we had to make a decision," he said.

Oracle is a big user of Sun's Java technology and says it's one of the main reasons it bought the company, though it hasn't given specifics about its plans.

Getting hired by Sun and being given the chance to work full time on JRuby was "pretty much a dream come true," Nutter said. The team got to work independently as a "satellite project," but with Sun's engineering resources behind them, including access to its Glassfish, NetBeans and JVM software.

JRuby has since gone through several releases and been deployed in some critical business applications, including an infectious disease reporting and management system used by the state of Utah.

"We really have managed to build JRuby into pretty much the best alternative Ruby implementation that's out there; we've got production deployments all over the world and lots of people really love it. We certainly couldn't have done it without Sun," Nutter said.

Engine Yard, which offers hosting for Ruby on Rails applications, is hiring the team because it's seeing increased use of JRuby by Java Web developers and lacks expertise in that area, said Michael Mullany, its vice president of marketing. A recent survey by Evans Data showed the number of Ruby developers increasing 40 percent from a year earlier, he said.

"I think one of the things that can take JRuby to the next level is having a paid commercial support offering and a real professional open-source offering around it," Mullany said. Engine Yard approached the developers about working at the company, he said.

Sieger had been leading Sun's Project Kenai, Nutter said, which allows developers to host applications in the cloud, a bit like SourceForge. He'll go back to full-time JRuby work at Engine Yard.

The fourth leading JRuby developer, Ola Bini, still works at ThoughtWorks, where he was hired last year, Nutter said.

A Sun spokeswoman confirmed that the developers' last day at Sun would be this week but didn't have further comment.

Nutter said he would continue to develop JRuby and support the community much as before. The next release, 1.4, is due around September, Nutter said. "We ended up moving it back a month because of this move," he said.

"One of the big focuses [in 1.4] will be doing for the Java side of JRuby what we've done for the Ruby side," Nutter said. "Over the past two to three years we've done a really good job of making JRuby into an excellent Ruby implementation, and now we want to turn our focus a little bit to making sure it's the best JVM language as well, and a first-class citizen on the Java platform.

"That includes making sure de facto standards like Hibernate work very well with JRuby, making sure new libraries and frameworks and standards from the [Java Community Process] work with JRuby as well as Java, and also, to a degree, making sure we can continue to improve JRuby's performance on the JVM."

The team will also do some work to make sure JRuby runs as well as possible in Engine Yard's hosting environment, he said.

The developers planned to announce their move in a blog post Tuesday afternoon, he said.