Recently, the Linux foundation produced a report which details the main sources of kernel development. Canonical, creators of Ubuntu, were outraged when they were accused of contributing only six patches in the last five years. This was later found to be erroneous, and in actual fact Ubuntu had contributed 91 patches. This is still minuscule when compared with Red Hat and Novell, the two biggest individual contributors, who together produce more than 20% of the kernel.
These statistics show that Red Hat and Novell undoubtedly play a large part in the development of the Linux kernel, but what effect this really has on the performance of each distribution is unclear. The nature of Open Source means that contributions made by Red Hat and Novell are available for use by all the other distributions. Both vendors have traditionally included heavily patched kernels, including much work aimed specifically at their target customers which may not be applicable to the more general requirements of the plain Linux kernel. The standard Linux kernel has to cope with a very wide range of systems and architectures, from tiny embedded devices to massive systems with hundreds of processors, so these patches are clearly of benefit.
Also of note should be the fact that more than a quarter of the contributions come from people not affiliated with any company, or affiliated with a small company. This shows the wide distribution of Open Source contributions, which ultimately strengthen the Open Source community.
Other Projects
Aside from the kernel, all Linux distributors have projects they have contributed to the wider Open Source community. The Red Hat cluster suite, including the gfs2 clustered file system, is probably Red Hat's largest contribution. Canoncial, creator of Ubuntu have the bazaar version control system, which has been rather overshadowed by Linus Torvald's GIT project. Novell have the previously mentioned AppArmor, and Debian is responsible for the apt package manager.
