Q:

Drupal modules be used without Drupal

Problem, can I use Drupal modules in my own PHP application? ( without setting up Drupal ). I searched a bit, there seems to be .zip file for the module, init where there are .inc files. 
Is it possible to use this without setting up Drupal ? 
I need to configure Solr search, Drupal seems to have a search API and thought I could use it.

A:

You can use the PHP solr library, instead of trying to hitting your brain on drupal modules files. With few extra code you can able to do indexing, searching ,etc. There is a good library https://code.google.com/p/solr-php-client/ . 
There is a good tutorial on Solr installation and usage in PHP. http://www.ibm.com/developerworks/library/os-php-apachesolr/

