H _ _ _ m _ n, Y a _ _ _ e e, _ _ t t _ _ _ h i p, _ h u t _ s & L a _ _ e r _ , R _ _ k , _ _ n d y _ _ _ _ , and _ _ r t s.
posted by Jasper Friendly Bear on Apr 7, 2012 - 28 comments

92 years young, the delightful Raymond Smullyan is a mathematician, logician, magician, concert pianist, and Taoist philosopher - who also pioneered retrograde chess problems.
posted by Trurl on Jun 26, 2011 - 22 comments

The annual Melbourne University Puzzle Hunt is back - and this time they need your help fending off villians with your puzzle-solving abilities. Anyone from anywhere in the world can compete in teams of 1 to 10 people (or you can see the puzzles for yourself and play at home). [more inside]
posted by divabat on Apr 10, 2011 - 7 comments

Rithmomachia: the Philosophers' Game. [more inside]
posted by Iridic on Jun 28, 2010 - 14 comments

Topology and Geometry Software by Jeff Weeks.
posted by Eideteker on Apr 22, 2009 - 5 comments

In Games, an Insight Into the Rules of Evolution. Carl Zimmer writes about Martin Nowak (previously mentioned here), a mathematical biologist who uses games to understand how cooperation evolved. [Via MindHacks.]
posted by homunculus on Aug 11, 2007 - 4 comments

A View from the Back of the Envelope - approximations and the fun behind them.
posted by Gyan on Oct 18, 2005 - 25 comments

Thinking Machine 4 explores the invisible, elusive nature of thought. Play chess against a transparent intelligence, its evolving thought process visible on the board before you.

From Martin Wattenberg (with Marek Walczak); they have been noted here before.
posted by e.e. coli on Oct 27, 2004 - 11 comments