You can launch a different app from your application on click of a button or something with the package name and if you dont know the launching activity of the application to be opened..You can use this
Intent LaunchIntent = getPackageManager().getLaunchIntentForPackage("com.package.address");
startActivity(LaunchIntent);
and if you know the launching activity also which you can see from the manifest file of the app to be open then use this.
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.setComponent(new ComponentName("com.package.address","com.package.address.MainActivity"));
startActivity(intent);