Custom apps are only available in the Pro subscription.
Even though Playr provides out-of-the-box support for displaying content from many online sources on your TV screen, there are still so many more sources that you might want to pull data from and present that on your TV screen in a nicely formatted way. This can easily be acchieved by creating your custom app for such a source.
When you create a custom app it will be available on all dashboards by default. From the custom app overview you can select the On dashboards option for a particular custom app to configure on what dashboards it should be available. Or you can also configure it the other way around: only select the dashboards on which you don't want it to be available.