In the past, having a device that only ran a single app (often called "kiosk-mode") was limited to certain hardware or relied on software from third-parties. With Windows 10 this becomes a lot easier, thanks to Embedded Mode. It seems this feature isn't very well known so I thought I'd share details of it with you here.
What it allows you to do is have the device run a single app. This is what happens with an IoT device. Embedded mode is enabled by default on devices run Win10 IoT Core and can be enabled on Mobile and Desktop devices too. Not only does this let you only access a single app when using the device but also enables other functionality such as background tasks that can run forever.
For more details, see the instructions on the IoT Github site http://ms-iot.github.io/content/en-US/win10/EmbeddedMode.htm