Simplest app can be created via https://gist.github.com/mathiasbynens/674099 e.g.
mkdir -p MyApp.app/Contents/MacOS
printf '#!/bin/bash\nsleep 5' > MyApp.app/Contents/MacOS/MyApp
chmod +x MyApp.app/Contents/MacOS/MyApp
echo "<plist><dict></dict></plist>" > MyApp.app/Contents/Info.plist
But more "appy" app can be done via the followning steps