I've spent the better portion of today playing online Hnefatafl, which is commonly known as 'Viking Chess', but should probably really be called Nordic Chess. A friend of mine picked it when we were in Oslo earlier in the year. I'm a bit of a chess nut, and consider myself to be a pretty decent player, but this game, which is sort of a mixture of Chess and Go, takes regular chess strategy and hurls it out the window. It's incredibly dense- each move has to be plotted almost to the end of the game.
In Chess, you can 'trade' pieces back and forth and still be relatively assured of your position- even down to the last few pieces. A bad move in Hnefatafl 'cascades' into a series of certain destrrrruction- you're never more than two moves away from losing (or winning) the game. It's definitely knuckle-biting fun.
Anyway, give it a go online (if you're into that sort of thing), it'll bend your brain backwards. If you want to meet me in Mile End Artspark for some kind of Hnefatafl show-down for money: you're on.

Had a go at the JavaScript version: it seems good. Unfortunately the English rules they point you to for the 'normal King' version have gone 404, but I think I get most of the basics.
I must find people to play Go against. Preferably people who are no good...
Thank you for linking to my hnefatafl-page.
The address has changed from
http://hjem.get2net.dk/Reinhold/hnefatafl_online.html
to
http://home20.inet.tele.dk/rnielsen/hnefatafl_online.html
Best regards
Aage Nielsen