Innovation in Open Source Software?

ndogg asks: "Many have said that there is a lack of innovation in OSS software, and tend to talk about the big projects, like Mozilla and the Linux kernel. However, I would contend that innovation is quite abound in OSS, but that the problem is the spotlight is rarely shown upon those projects that are truly innovative. For example, I would contend that Data Display Debugger (DDD) and The Boost C++ Libraries are quite unique and innovative projects. What OSS projects do you feel are innovative, but underapreciated?"