Download tiles for off line App

I wish to download tiles in order to create an off line app with leaflet.
How can I do that?

The preferred method is to install the rendering tool chain and render them on your own machine.

For very low volume use, a simple bit of reverse engineering, or just looking at the JOSM configuration will tell you what the tiles are called, and the rest of it is a leaflet/OS issue, not an OSM one.

Where do I find the rendering tool chain and documentation about the process?

Whilst I haven’t done this myself, describes one setup for rendering map tiles.