Just develop a normal app and then add a couple of lines to the app's manifest file.
First you need to add the following attribute to your activity:
android:launchMode="singleTask"
Then add two categories to the intent filter :
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.HOME" />
The result could look something like this:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.dummy.app"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="11"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.dummy.app.MainActivity"
android:launchMode="singleTask"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<category android:name="android.intent.category.DEFAULT" />
<category android:name="android.intent.category.HOME" />
</intent-filter>
</activity>
</application>
</manifest>
It's that simple!