Sure, there are a couple of popular power saving libraries, and they have been around for years. But none that I have seen are sophisticated enough to let you to use all the techniques discussed in Gammon's tutorial.
There is nothing like "delay while power saving", as the MCU clock must be turned off. You have to put it to sleep, with some sort of interrupt to wake the MCU. Most people use the watchdog timer to effect a short wakeup period. Google "Arduino watchdog wakeup" for some examples.