title: How can I create Android Application plugins/extensions that can be installed as an APK or from market?
body: <p>I'm actually investigating the possibility to have an application that fulfill the following requirements:</p>
  
  <ul>
  <li>The Main Application may have 5 deactivated functionalities</li>
  <li>If you try to use a deactivated functionality, the application invites you to download an extension that can be installed as an APK or from market.</li>
  <li>Once the functionality is installed, it becomes activated and then it can be used. </li>
  </ul>
  
  <p>So we can have some free/not free functionalities. I've already seen such a behavior in some applications but I don't remember the name.</p>
  
  <p>Is there something in the Android SDK to be used? how it can be implemented?</p>
  
  <p>Thanks for your help.</p>