OpenTileServer is a script developed by the petiole team.
It allows you to set up your own OpenStreetMap server quickly and easily.
Combined with petiole, or any other Open Source map application, it affords developers and any user the ability to have a 100% Open Source stack for their mapping applications.
Learn more at http://opentileserver.org
If you are just looking for map tiles that are publicly available, there are a number of options: