Current geeky distraction

SimSig, a British railway signaling (US: railroad dispatching) simulator. From what I can tell it started life as a free-demo-shareware product until Network Rail noticed it and contracted with its author to turn it into an internal training program, and the formerly-paid content got released as free-as-in-beer (so remember to note the registration codes from the download page). The two maps I've tried so far are the Liverpool Street map (not too exciting) and Didcot (actually pretty busy).

(This falls into a bizarre category of things that must be too geeky for anyone but me to appreciate, except that two or three people I've mentioned it to have come up surprisingly interested.)

( Brief user manual )

The system also has the ability to have multiple networked players dispatching adjacent districts, if the maps are set up for it (the Swindon-Didcot-Oxford-Reading maps at least apparently are). LAN party, anyone?