Every so often a new app or website will suddenly appear on the tech scene and get everyone talking. You might remember Ello, dubbed the "anti-Facebook", which exploded on to the market in late 2014 only to be mostly forgotten about by 2015. And then Meerkat, a live video streaming app which gained early momentum but is now overshadowed by Periscope, the Twitter-owned app that essentially does exactly the same thing. More recently, there was Yo. An app that only allowed people to say Yo to each other.–BBC