These are various functions and helpers to make life in PHP easier. Some of the helpers are inspired by different frameworks and libraries like Rails, Webrat, RSpec and many others.
You can either include the individual files into your application or put them somewhere in your include path. Make sure you conform to the license.
These files are licensed under the GNU Lesser General Public License. You can read more about it at http://www.opensource.org/licenses/lgpl-2.1.php