shared cartodb contributions.
For background, see here: http://gis.stackexchange.com/questions/134544/in-cartodb-best-way-to-have-a-table-with-multiple-contributors/134562#134562
The proposed solution is here: http://blog.cartodb.com/read-and-write-to-cartodb-with-the-leaflet-draw-plugin/
A visible (but disabled) example is here: http://bl.ocks.org/matallo/130b969a6cc76939985d