I've talked about the Apache Harmony project, an effort to develop an open source implementation of the J2SE 5.0 spec. Some question why computerdom needs an open source Java when you can just download the JRE free from Sun.
Floyd Marinescu has a good summary on his blog, Dynamic Semantics: clear problems that having Apache Harmony will solve. It summarizes the comments on the IBM commits a full time employee to the Harmony Project thread on TSS. (I commented on the same news in IBM Joins Project Harmony.)
An interesting point to me is that Linux folks are apparently interested in having a JRE be part of the OS install. Back around 1990, legend has it, Sun was interested in having ParcPlace Smalltalk built into SunOS, but the parties never worked out the licensing. Back when Oak became Java, I thought part of the idea was that Solaris would have Java built in and therefore be able to run any Java program (without the Solaris user having to separately download and install the JRE). Now it sounds like the Linux folks may actually, finally make this happen. Cool.