AirTab claims that its first eponymous product is an ultra-lightweight on-the-go secondary display. It measures 15.6 inches diagonally, and also has a SKU with a touchscreen. This device has been launched via Kickstarter, and has amassed 100% of the backing looked for in just 1 hour.
https://www.notebookcheck.net/The-AirTab-portable-monitor-has-reached-its-crowdfunding-target-in-just-1-hour.476643.0.html