A RTOS is a key piece in whatever modern electronic embedded design. With the current trend of very powerful microcontrollers, like LPC10 family from NXP (Cortex-M0), with a sub 1 USD range, makes sense to use RTOS in the development, for sort development time, reutilization and scalability.
The Keil RTX is a royalty-free, deterministic Real-Time Operating System designed for ARM and Cortex-M devices. It allows you to create programs that simultaneously perform multiple functions and helps to create applications which are better structured and more easily maintained.
While it is certainly possible to create real-time programs without an RTOS (by executing one or more functions in a Super-loop), there are numerous scheduling, maintenance, and timing issues that an RTOS like the Keil RTX solves for you. For a more detailed comparison between RTOS and Super-loop, take a look at the advantages of using an RTOS.