It may be simple for brands to create their own web storefronts today, but doing the same for mobile is a far more difficult task. With that challenge in mind, David Tisch, an angel investor at Box Group and former TechStars NY managing director, set out to create Spring, a mobile marketplace that gives brands a simple way to let consumers shop with them. After a year of development, Spring is launching today on the iPhone. And while there’s no shortage of shopping apps out there, it’s actually doing something truly different.