Although there is not a built-in power saver setting, the moto x uses a Qualcomm chip, and the Qualcomm app "battery guru" for snapdragon chips has a low power setting.
In the battery setting there is the battery saver, but it is only for low battery level. I use AutomateIt to regulate things that will help my battery life on my OG X. I shut off mobile data when connected to wifi to shut off the radio, I use the rules to regulate the screen brightness when I'm plugged in and when I'm not, you can shut off the background sync when the screen is off, etc.