Grammar App / Online

Hi folks - I've started learning German - building my flashcards, etc. I need to find a good source for German grammar and honestly paper books don't work for me and doing something on Kindle would be something of a poor substitute. Does anyone know of any apps that are essentially grammar books? I checked in Google Playstore but there wasn't an obvious "winner" i.e. something that could replace a traditional book. Thanks for your assistance, Paul

* Originally posted by bricin.