Seattle-based Farecast has launched a public beta of the company's airfare prediction website. The company announced this morning that travelers flying from Seattle and Boston can use the company's site, at www.farecast.com, to get free airfare predictions. Farecast said that the predictions cover 120 domestic markets from those two cities. Farecast is developing technology to predict the trend of airline fares. Farecast is venture funded by Greylock Partners, Madrona Venture Group, and WRF Capital.