Basic App Bootstrap
ForBetterWeb makes some very beautiful, modern themes and here is a free theme built on Bootstrap. It's a simple, but functional landing page for your app. The design looks professional and high-end. It comes with 5 color schemes, and there are vertical sections to highlight app features or screenshots. There are also social and app store links for iOS, android and chome. Notice this theme's clear balance, and beautifully aligned elements.