Some students wait tables or landscape gardens to pay for college. Jack McCarthy scoured Midwestern vintage stores for the ugliest Christmas sweaters he could find. McCarthy, 22, bought whatever he could get his hands on, usually for a few dollars apiece, then sold them online for more than $20. At one point the operation was pulling in $100,000 a year—money McCarthy used to graduate from Babson College debt-free. Shopify Inc. helped him do it. The Canadian company provides websites, payments, shipping and more for 500,000-plus online merchants and, less than three years after going public, has a market cap of $10 billion—making it roughly the size of Twitter Inc. or Square Inc. Shopify’s thesis is relatively simple: People all over the world have the brains and energy to start successful online businesses, but lack the tools. Shopify lets them try out online store ideas for $29 a month, and the first couple weeks are free. Many fail, but those that find a market start to grow. The more successful they are, the more money Shopify makes through transactions fees and higher-priced subscription tiers. “Such a minimal barrier to enter is one of the reasons why Shopify is growing like crazy,” McCarthy says by phone from Holland, where he’s traveling and doing e-commerce consulting on the side. Read more at Bloomberg.