I have several contributions to the Linux Kernel Crypto Section. Crytpo is a great place to contribute to the kernel. The maintainers are great to work with.
The LinuxICC project was a project building the Linux Kernel with the Intel C Compiler. The Intel C Compiler generated different warnings. There were a decent amount of Linux cleanup patches which generated by the project. Might relaunch it sometime using the Clang compiler.
This was a project that ran the Linux Kernel through the PMD project's Cut and Paste Detector/CPD. There is a lot of duplication in the kernel because of related architectures (amd64 and i386 both duplicate a lot of code).