It's called a launcher, which is a normal APK application. It's a normal Activity
which reacts to a certain Intent
.
You can create another one, and install it on your phone. When you press the home button it will ask which Launcher to use.
<activity
android:label="@string/app_name"
android:name=".ClassNameOfYourLauncher">
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter >
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.HOME" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>