Question: Looking for a cross-platform AR SDK that supports instant tracking without pre-defined markers.

If you're looking for a cross-platform AR SDK that supports instant tracking without pre-defined markers, Wikitude Augmented Reality is a top contender. It offers Instant Tracking (SLAM) for markerless tracking, as well as a variety of other advanced features like Image Tracking, Object & Scene Tracking, and Geo AR. Its support for Unity and native APIs for Android and iOS development, and its support for a broad range of devices, makes it a good option for complex AR projects in a variety of industries like retail, education and entertainment.

Another good option is EasyAR, which has a modular and flexible API that's centered on the Sense SDK. EasyAR has features like spatial mapping, motion tracking, and multi-sensor fusion for better tracking. It also supports 3D point clouds and meshes, 3D object recognition, and a city-scale AR cloud service for large-scale data collection. With its support for iOS, Android and MR eyewear, and its multiple subscription levels, EasyAR is good for a broad range of development needs.

Blippar also has a full AR platform with tools for creating AR content without programming. Its Blippbuilder Studio offers a graphical interface and supports marker, surface and face tracking. Blippar's WebAR SDK works with popular frameworks like PlayCanvas and A-Frame, so you can build more advanced AR experiences. Blippar's in-house studio also offers custom AR development services, which can be useful for businesses that want to incorporate AR into their plans without having to get too technical.

If you're interested in web-based AR, 8th Wall offers a platform for building immersive WebXR experiences that run in ordinary web browsers. It's good for a broad range of use cases, including e-commerce and entertainment, and doesn't require people to download separate apps. That makes it a good option for industries like marketing and retail where convenience is important.