Founder on Twitter's sketchy start
It's got more than 250 million users worldwide, including some of the globe's most powerful people - but Twitter had humble beginnings on the back of a scrap of paper.
Its co-founder Biz Stone has written a book about the launch of the micro-messaging site, which has grown into a multi-billion pound business.
He told BBC's Newsnight: "We said lets just work on something that we were interested in. That's all it was. It was just joyful."
- From the section Technology