Katie Melua's song, "9 million bicycles" was penned in an age when China was known as "the Kingdom of bicycles". Since then, improved transport options and increased wealth have led to a decline in their use, but with the launch of Mobike in Tianjin last month, the number of people pedalling the streets of the city are set to increase once again. The popularity of companies like Mobike is part of a boom in what is loosely called "the sharing economy", a term for a range of online services that connects owners of underused assets with others who are willing to pay to use them. Of course, riding someone else's bike for an hour doesn't have the same romantic connotations that is implied by Katie’s song. Love is one area where sole ownership is still preferred, but for a growing range of transport, accommodation and office spaces, people are increasingly choosing to share. The principle is, why pay through the nose for something when you can rent it more cheaply from a stranger online?