mcmap is a Minecraft automap that works by proxying the connection between the Minecraft client and server, and extracting the world information from the traffic.
I wrote the initial version in late 2010; other people have worked on it, too.
Caveat: it might not always be very speedily updated to be compatible with the latest Minecraft versions.
Here's a rather old (and probably outdated) look at how one could
simulate digital logic circuits with OpenTTD. Includes the fastest
four-bit ripple-carry adder ever: takes about two months (of in-game
time) for the carry information to propagate.