Embedded system
Common examples of larger kernels are Embedded Linux and Windows CE.  Although these do not have the tight time limits needed for a strict real-time system, they are becoming more common, especially for more powerful devices such as Wireless Routers and GPS.  They allow re-use of code in the public domain for Device Drivers, Web Servers, Firewalls, and other code.  Software developers that are more comfortable writing applications for PCs will find this more familiar as well.  If needed, an FPGA or other special hardware can be used for things that do need tight time limits.