A CO DOWN firm has developed an app marking out the Edinburgh Book Trails. Origin Partners in Holywood created the app with Scottish firm Purple TV. Origin Partners commercial director Jonathan Kelly said: "Origin Partners teamed up with Purple TV to develop a series of City Adventure Apps that would come under the brand 'Purple Trails'. By marrying the latest digital technology with traditional television production, the objective was to create a platform that would allow people to interact with cultural and sporting heritage in a 'fun' and 'engaging' way." The app supports the Edinburgh International Book Festival and has been named in The Guardian's top 20 apps.