After a few years of development here are my XML projects. I used Curl to pull sections of data from websites. Since they are a combination of PHP and Curl, the data is always up to date. You would use this if you intend to make an app for Craigslist, Newgrounds or Primewire for Android, iOS or Windows.
To use this data you create an XML reader that will get this data from the site, then put it in to your app and design it how you want, making an unofficial app! I included an example index file to show you which arguments each file can take to filter and display the data you want.