Yoga App for Home

[harknesswitch]

I'm a newbie to yoga, unfit, over weight with a bad knee (probably down to being over weight) and really need something that's low impact that will strengthen my muscles:

Can anyone recommend a good yoga app, for beginners that I can easily do at home?

I'm very similar as was recommended Fightmaster's beginners course on Youtube. It's really good and helped to strengthen up my unfit body

Down dog yoga is excellent, you can make the class as long or short as you like. Focus on various things like core strength or hamstring stretches. The music in the background is fab.