A little more than a year ago, Prashant Singh was an engineer at Microsoft's Mountain View campus working on projects including Internet-connected televisions and the Xbox. But for the past year, his career has taken a civil service turn. The 31-year-old engineer spent 2012 designing a public transit tool and other technology for the city of Detroit. Through the San Francisco nonprofit Code for America, Singh took a sabbatical of sorts. As fellows of the effort nicknamed the "Peace Corps for geeks," Singh and 25 other techies fanned out for a year across the United States to help municipalities develop...