I heard about the guy who made a (seemingly)turing complete computer in DF. Is this serious or is it a hoax?
I haven't looked at it in depth, but it is certainly possible - there are other similar examples such as creating a turing machine in Conway's Game of Life: http://rendell-attic.org/gol/tm.htm
There are enough mechanisms in DF such as switches with open and closed doors, pumping water and holding it in places etc. for it to be plausible.