Think about all the sports we play with sticks, paddles, bats, and so on: Baseball, golf, tennis, hockey, ping pong, etc. Now imagine being able to play those sports in virtual reality with super-accurate tracking of actual sticks, paddles, or bats.
That's the idea behind the new ViveTracker, from HTC. Meant as an add-on for HTC's high-end Vive VR system, the tracker opens up a wide variety of new virtual reality experiences, making it possible for developers to build games where, for example, you can swing an actual bat at a baseball instead of the standard, bulky, Vive controller, and do so with highly accurate tracking of your swing. Though the tracker was just introduced and there aren't all that many implementations of it yet, it's easy to imagine how it could be used in the future to augment many different VR experiences and give users the feeling they're really playing, say, baseball.