Google has been ordered to open up its app store to rivals following a major court case in the US. Last year, a federal judge ruled the tech giant was running an illegal monopoly in how it controlled the distribution of apps on its Android operating system and via the Google Play Store. Now, in the final ruling on the case, Judge James Donato has ordered Google to open up the Google Play store in the United States for three years, including allowing third-party app stores to be distributed from within Google Play, and giving third-party app stores access to the full catalogue of Google Play ap…