title: android: how do i open another app from my app?
body: <p>I understand how to use intents and startActivity() when opening another activity within my own app, but how do you start a different app? specifically: </p>
  
  <ul>
  <li>How do you determine if the user has the needed app installed on their device?</li>
  <li>How do you start that app?</li>
  <li>How do you pass parameters to that app?</li>
  <li>How do you find all this info out for a specific app (say Adobe reader, or google maps)?</li>
  </ul>