requires shapefile-js plus if you want it to be done in a worker, you'll need catiline.
usage:
new L.Shapefile(arrayBuffer or url[,options][,importUrl]);
L.shapefile(arrayBuffer or url[,options][,importUrl]);Options are passed to L.Geojson as is. First argument is either an array buffer of a zipped shapefile,
the url to a zipped shapefile, or the url to file.shp (this assumes file.dbf exists). The importUrl parameter allows you to change where a worker loads in shp.js when using catiline and defaults to shp.js.
To easily try this out using your own shapefile, see the demo at leaflet.calvinmetcalf.com, where you can drag-and-drop your own shapefile and have it displayed on the map.