Google Analytics

Add tracking code () into the "..." (commonly in head.html) of your meteor app.

You can find your tracking codes at Admin -> User Management -> Tracking Info -> Tracking Code.

Get real-time data (such as on-site user number) at Reporting -> Real-Time -> Overview.

Kadira

meteor add meteorhacks:kadira

Add the following codes into server/kadira.js:

Kadira.connect('<App ID>', '<App Secret>');

get your AppID and App secret at Kadira -> [Your App] -> Settings.

Then see read-time statistics on its dashboard.