battini:
"CrossRoads"i am a student doing internship on car2car communication using arduino atmega168 franzis... is there any possible to use RTOS in this board
thanking you
Why do you think you need an operating system? When googling i can indeed find operating systems for arduinos (but not sure if they'll work on the arduino you selected, since you've got a fairly light avr in there). This is a tiny microcontroller (not micrprocessor) with 1kb of ram (Kb, not Mb or Gb, it has less than 1 millionth the amount of memory compared to an average pc these days).
as others mentioned, there are indeed 'OS'es' available, but they're more in the range of libraries that allow for certain extra functionality, if you don't need that functionality, don't use them, or assume you need them.
Some people mentioned that it might be a trick question of your boss, and i do agree. If you don't know what a microcontroller is, and how to use one, you might believe you need an OS on there (you really really REALLY don't). Either that or he doesn't know what he's talking about either, and is looking for something that isn't needed, and is assuming the arduino is far closer to a modern computer than it actually is.
Why don't you follow the suggestion someone else made in this thread: start doing some basic arduino tutorials, see how to program it, and realise that you can get it to do things without needing an "OS". An OS is required for abstracting the modern microprocessors and near infinite possible hardware combinations to something a bit easier to handle. Not for managing a very basic 8-bit microcontroller.