Yahoo is giving away tools to mobile app developers in a move to increase revenue from mobile ads, an area where the tech giant has fallen behind its rivals. Yahoo is offering to distribute ads in other mobile apps besides its own and plans to keep 40 percent of the ad sales on those apps. Besides that, Yahoo also is trying to plant its search engine inside other apps so it can display ads alongside the results. The changes were announced Thursday at the company's first conference for the makers of mobile applications. CEO Marissa Mayer described the extension of Yahoo's mobile platform as a "fork point" in her effort to make the company an even bigger player on smartphones and tablets. "Yahoo really fell behind the times in the evolution of mobile," she told reporters and analysts. "I feel like we have really caught up now."