Drupal is a great platform for managing content.

Why not manage your collections in Drupal.

Yesterday, someone on groups.drupal.org proposed a Drupal ILS: http://groups.drupal.org/node/13964

Very cool idea.

Although there is no reason to try and compete with Koha or Evergreen, I think Drupal could be very powerful for smaller libraries or special libraries that cannot afford the hardware and maintenance of even these "free" ILS.