Later this year, Apple will release OS X 10.10 Yosemite, the latest version of its Mac desktop operating system. It will run on all the same Mac models as OS X 10.9 Mavericks, and will be a free download and update.That's all expected, but there are some unexpected changes coming with Yosemite. For a start, Apple is offering a public beta of the operating system, something Apple hasn't done since it was preparing to launch OS X in 2000. Anyone can apply, but bear in mind this release is for testing bugs, not a demo of the finished OS. If you apply and are successful, make sure you follow Apple's advice on backing up and installing somewhere safe carefully.I've been trying a beta build provided by Apple, though, and have had a chance to dig into the more important changes for most users: the extra features.