An unabashed promulgator of the Internet and its democratic potential, Doctorow explores the benefits and consequences of online systems in this provocative collection of six mostly long stories. “When Sysadmins Ruled the Earth” is a moving chronicle of widely dispersed techno-geeks laboring to keep the World Wide Web running as an epitaph to an earth devastated by a bioweapon apocalypse. In “After the Siege” — the bleak chronicle of a modern siege of Stalingrad — the horrors of war become fodder for a documentary film crew’s reality-based entertainment. Two tales riff on classic sf themes: “I, Robot,” in which Isaac Asimov’s positronic bots are cogs in a dysfunctional totalitarian state, and “Anda’s Game,” a brilliant homage to Orson Scott Card’s Ender’s saga, in which a role-plaing enthusiast finds herself immersed in a surprisingly real world of class warfare fought online by avatars of game players. Most “meat”-minded readers will find much to savor.