Chameleon is a modern mobile UI kit for Sketch and Photoshop. With 100 beautiful screens in 7 categories, 15 unique themes, 60+ icons and hundreds of neatly organized components you can easily create design for your mobile app.
The golden ratio should not need any introduction to those who have studied math and design in school. Some designers apply these mathematical concepts to come up with more visually appealing works. This infographic from companyfolders.com covers a few golden ratio facts: