The NODE is a streaming unit you can add to any home audio system just like a CD player. It can access audio files on your network (including HiRes), use Apple Airplay2, has two way aptX Bluetooth, plus, works with just about all of the major streaming services including Spotify, Tidal, Qobuz, Deezer, Amazon Music, iHeartRadio, TuneIn, and many many more. It can also playback MQA files and works great with Roon.
The NODE also gives you one more audio input that can be used as a digital or analog input, plus, you get a subwoofer out. Unlike many units that just have a fixed sub out, the Bluesound app gives you the ability to fine-tune the crossover.
Some people use the NODE with a separate power amplifier as you can change its output to be variable for this use case.
If you take a NODE and add power to it, you get the POWERNODE. The POWERNODE is designed to just add a pair of speakers and is basically like a small streaming integrated amplifier.
Another similarity between Bluesound and Sonos is the fact you can sync many units in your home for whole-house music. This is really simple to do in the app and allows you to play the same — or different —music throughout your home.