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 , 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.