This started off as an idea on TDIClub Forums
and gathered a lot of attention. There are numerous tuners that tune diesel engines but those all work on remapping the original software. A lot of it is guess and check as there are often 3 maps that 'do' the same thing depending on Manual, Automatic or 4WD. Unlike the gasoline world with RusEFI, FreeEMS, MegaSquirt, etc I haven't found many (any actually) that were designed specifically for diesel engines.
The Bosche EDC15, 16 and 17 run a large portion of diesel engines out there. Almost everything from the Volkswagen Auto Group (VW, Audi, Skoda, Seat) plus some Mercedes-Benz, Alfa Romeo, Peugeot, Citroen, Opel, and on.
My project is in its complete infancy. No code has even been written and I'm narrowing down what development environment, tool chain, chipset, OS, etc to go with. I stumbled on Russian's website and then found this one.
Someone else out there already made Arduino code for his TDI swap: http://dmn.kuulalaakeri.org/dmn-edc/http://openedc.info/