Google now

 Google now  is a proprietary Google tool/service that keeps track of events and shows information cards from various sources with updates as needed.

It attempts to act somewhat as an automated "personal assistant".

More documentation: https://support.google.com/websearch/answer/2819496

What type of cards does it show?
Updates within Google now are shown as cards:
 * Boarding Pass - retrieved from Gmail
 * Flight Information - from flights from boarding passes
 * Package Tracking - retrieved from Gmail
 * Sporting events (and scores) - manually added from the settings configuration
 * Appointments - retrieved from Google Calendar
 * Travel to your next destination - from airline confirmations emails in Gmail
 * Weather - from Geolocation API on the device

This information is gleaned from any number of sources, from your Inbox, Calendar and also from web sites you visit frequently.

Articles

 * http://www.wired.com/2015/05/google-now-io/