I downloaded JDiskReport after seeing the write-up on Tim Bray's blog, ongoing. While it's not a unique idea (for example, see File System Visualizer), it's a nice implementation. Notice that the hyperlink to JDiskReport there points at a ‘.jnlp’ (Java Network Launching Protocol) file—that is, the application is distributed by Sun's Java Web Start framework. Mac OS X had no trouble with this. Mike Gratton reported that he tried it on one of the 4 billion flavours of Linux, and that it didn't work. So your mileage may vary.