Vuforia is a platform used to create apps for Augmented Reality (or AR). Hundreds of thousands of companies employ it across different industries, from Automotive to Entertainment, Healthcare, Electronics, Architecture and many others. Though it is currently restricted to Android, iOS and Microsoft’s UWP (including HoloLens), it recently added support for Unity.
Now I’ve seen a few experiments conducted on these forums by indie devs with AR, so I think if Unreal added Vuforia support, it would open the door for a lot of projects.