Jamboard is an amazing collaborative digital whiteboard. It is free and all Jams live in Google Drive. You can access it at jamboard.google.com, by going into Drive, select 'New', 'More' then find Jamboard in the list or your Google "Waffle" apps.
Jamboard is also available as an app at the Google Play Store or Apple Store. The Jamboard app can be used on any iOS, Android, or app enabled Chromebook.
Jamboard Basics
Get Started with Google Jamboard