HIIT (High Intensity Interval Training) exercises are great for burning fat and building lean muscle. These exercises force you to work hard in short, intense spurts giving you greater after burn (the amount of calories you burn after your workout is over).
HIIT exercises give you the combo of strength training and cardio in one workout. And cardio is the best fast burner.
I built my HIIT exercises (Core Blast, Sexy Booty, 20x10) from exercises I found here and at ab-workouts-guide.com if you like em checkout Cardio Fight Club HIIT, Core Abs & Stretches, Strong Inner Warrior, and MAX Tabata Test they're fun and challenging.
If your looking for a great diet app try Noom or Lose it too name a few.
Good luck and God Bless!