Good day,all

I have some troubles about time management and resource management. And there are many information shows that I should 
use RTOS to do that. However,my time has not permitted my own research, I am here today to find some feasible 
suggestions.
I am now using low resource microcontrollers--PIC MSP430(this one: http://www.kynix.com/Parts/3960939/MSP4301103IPWR.
html ) and looking for RTOSs that I can use. My point is:
Resource cost of system
Advantages of system
Disadvantages of system
Implementation Tricks
Situations the RTOS should/should not be used in.
Is QNX suitable me here? This is the one I am considering about.

I do not use systems like the arduino, the projects I work with cannot support the cost of such a system.
Thanks in advance for any suggestions.