How Fast it is Going, Who is Doing It, What They are Doing, and Who is Sponsoring It ?

Since 2005, over 3700 individual developers from over 200 different companies have contributed to the kernel. The Linux kernel, thus, has become a common resource developed on a massive scale by companies which are fierce competitors in other areas.

The kernel which forms the core of the Linux system is the result of one of the largest cooperative software projects ever attempted. Regular 2-3 month releases deliver stable updates to Linux users, each with significant new features, added device support, and improved performance.

Reference doc is available at  here or do a Google search for more info.