Rumored for months, Microsoft has formally announced its answer to Apple?s Siri and Google?s Voice Search/Google Now: Cortana. Danny Sullivan is at the Microsoft Build Conference and live blogging it. Cortana appears to be sassy like Siri and can perform many of the functions that Google Now does (providing reminders and notifications regarding dates, meetings and so on). It appears to have numerous manual personalization capabilities as well. Cortana will also interact with and can launch apps on the device (like Siri or Google). Showing Cortana?s smarts, there was apparently an example of a restaurant search where Cortana offered content from Yelp ? Yelp and Microsoft have a deal ? rather than Bing. There was also an example of how reminders can be tied to particular individuals: At its core, Cortana is ?powered by Bing? and will ?completely replace? the search button on Windows Phones. It thus becomes a voice-search front end to Bing?s index and capabilities for Windows mobile devices. Siri can search the web (via Bing) but that process isn?t fully realized. Google?s Voice Search offers a generally better web search experience than Siri but Google?s ?assistant? functionality isn?t fully integrated or realized itself. Cortana appears to be quite sophisticated though I don?t yet see a clear breakthrough or differentiating feature. So far it?s mostly catch-up to Apple and Google. (Perhaps the pitch is that it offers a marriage of the capabilities of both.) However, I have not had an opportunity to use it yet. Regardless, Microsoft had to offer this on Windows Phones if it hoped to remain competitive. Cortana is launching in beta in the US (with 8.1) and will expand to other international markets over time.