Apple’s new XCode 3.0 development environment for Mac OS X 10.5 “Leopard” includes Sun’s DTrace technology.

When you need a bit more help in debugging, Xcode 3.0 offers an extraordinary new program, Xray. … Truly track read/write actions, UI events, and CPU load at the same time, so you can more easily determine relationships between them. Many such Xray instruments leverage the open source DTrace, now built into Mac OS X Leopard.

Update: Bryan Cantrill lets the cat out of the bag, Mike Shapiro has more technical details, and Adam Leventhal has pictures of Apple’s DTrace team.