network monitoring system

anyone can advice the most appropriate NMS for the servers? please send me a link or guide thanks guys :)
nagios comes to mind first, but as you have not specified any purpose, perhaps you find something among the mentioned candidates here:
monitor all of my servers to check their status in a specific time
This again is not specific enough, if you e.g. only want to monitor up-time, there are e.g. simple web-based tools. If you want to monitor particular services on each server, you can also use what comes built-in to various panels. Once you have decided exactly what to monitor, it will be easy to narrow down the list of tools.
i talk to my boss and he said that basically we are focusing to monitor the service and also the memory the ram, do have a better recommendation than nagios? @frm.mwz