An AppNexus IPO comes amid a public market dry spell — and controversy

AppNexus, considered to be the hottest name in the ad tech industry, has been on IPO watch for a while.Ever since it raised venture capital at a $1.2 billion valuation in August 2014— joining the " unicorn" likes of Gilt Groupe, MongoDB and Vice Media — observers figured it was only a matter of time before the New York-based startup filed paperwork for an initial public offering. The New York Business Journal, for example, ranked AppNexus on its list of 16 IPO candidates for 2016 bac