Kore was the most popular Ragnarok Online botting program, but has been abandoned since 2003. Kore.pl and the original X-Kore are no longer available for download, and the Kore forums are shut down. This is because the original author of Kore, Kura, has lost interest in Ragnarok Online. I recommend you to use:

VisualKore - a userfriendly Ragnarok bot with graphical user interface.

It is a successor of Kore.