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.
mcmap has a GitHub repository.
robotfindskitten is a
Zen simulation that has been ported to incredibly many sorts of systems.
In it, you assume control of a robot, looking for kitten amongst many non-kitten items (NKI).
rfk86 is a port of it to the TI-86 graphing calculator.
It has its very own website.
Here's a rather old (and probably outdated) look at how one could simulate digital logic circuits with OpenTTD.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.