When I was at Villandry the other day I spotted one of the gardeners using a very nifty tool. It looked just the thing for the soil in our argilo-calcaire (clay-chalk) vegetable garden so I stopped to talk to the gardener and ask about the tool.
He told me it is called a fourche-bêche, or sometimes a grelinette, after the inventor, André Grelin. Far from being homemade, as I had assumed, they are available commercially, so when I got home I looked them up.
They are very popular in the organic movement because they cause the minimum soil disturbance and take very little effort to use. I'm completely sold, and if I get any birthday money (hint, hint...) I will be buying one of these (they cost a bit over €100 if you buy them online and have them delivered from the French manufacturer Ducoterre).
According to their blurb they are ideal for difficult soils, allowing them to be worked without damaging the soil structure or straining your back. They are also good for working compost into the soil, harvesting root vegetables and weeding.
Apparently they are called broadforks in English.