Nintendo Switch Online app is available (but not yet functional). Edit: Correction, the article below says it was giving them a Server Maintenance error, but it's working for me.
http://kotaku.com/1797040718
iOS: https://itunes.apple.com/us/app/nint...e/id1234806557
Android: https://play.google.com/store/apps/d...ndo.znca&hl=en
Edit: When they talked about inviting people via FB/Twitter/etc with the app, I thought they meant just inviting to be on your friend list. This lets you invite people to the game lobby you're in via a URL that you share from the app. That's nice.