What surprised me was that my brother wasn't planning on buying a Sonos system. Around Christmas, he'd taken the Chromecast plunge by putting cheap streaming dongles into his home's guest rooms, and that's when he heard about Chromecast Audio's Sonos-like functionality. The idea being, you can stick Chromecast Audio dongles wherever you want in your home and connect each one to a 3.5mm speaker. Once they're all powered on and connected to your wireless network, you can play synced audio on all of them by simply hitting "play" on any supported app (and there are a lot of apps).
Read more: http://arstechnica.com/gadgets/2016/04/sonos-on-the-cheap-how-chromecast-audio-breathes-new-life-into-old-speakers/