Virtual worlds are endlessly mutable. As are the wildly implausible schemes their boosters concoct for making money off them. The latest idea Linden Lab has for Second Life: Profit, in some vague, unspecified way, from the world's free 3D design tools. The perpetually gullible BusinessWeek bought this story , pointing to examples of toy designers and architects building digital models and showing them off to customers in Second Life. There's a certain beauty to it: An entrepreneur's fantasy, used to peddle other entrepreneurs' fantasies. Not that there's much of a business here, since Linden Lab gives away its design software.It does suggest a graceful exit strategy for Linden Lab's investors, which include Benchmark Capital: They should persuade Autodesk to buy the company before its free design tools erode the market for that company's profitable design software. Not that I think that Second Life actually poses a threat to the AutoCad franchise — just that Mark Kingdon, Linden's adman-turned-CEO, is slick enough to make the pitch.