Thinking Machine 4: Play Chess Against a Virtual Master
Would-be Kasparovs can play an artificial intelligence program of average ability. You can actually see your silicon opponent think out its next move as it traces colored strands of potential strategies across the board.

Universcale: Understand Those That Cannot Be Physically Compared
How many times smaller was Tyrannosaurus rex than the Milky Way? How many times larger is a sequoia tree than an amino acid? This amazing Flash site makes us feel, well, small.