The new OpenNTF Domino API demo application is a Vaadin web application, available either to be run with CrossWorlds on Websphere Liberty or wrapped in an OSGi plugin to be run on Domino.
To use the CrossWorlds version, right-click anywhere in the Enterprise Explorer view and select Import > Maven Projects. Navigate to the folder containing the pom.xml of OdaDemoAppLiberty.
If you get any errors with regard to j2eeenabler, try closing and re-opening the project. If that doesn't fix it, in Window > Preferences go to Maven > User Settings and note the location of your local Maven repository. Go to that location and check org\openntf\xworlds\webapp\j2eeenabler folder exists. If not, extract the j2eeenabler.zip to that location, then close and re-open the project.
Once there are no errors, right-click on the server in the Servers view and click Add and Remove..., then select ODA_DemoApp and click Add>.
Now start the server and the application will start.The console will show the URL the application has started at, by default http://localhost:9080/ODA_DemoApp/. Open that URL in the browser and the demo application will load.
Sometimes the startup of Liberty times out. If it does, just retry.