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."