AR Core is described as 'is the Augmented Reality Library made by Google'. There are four alternatives to AR Core for a variety of platforms, including Android, Windows, iPad, iPhone and Linux. The best alternative is Wikitude. It's not free, so if you're looking for a free alternative, you could try ARToolKit or MyWebAR.com.
Augmented Reality Mobile App - Wikitude World Browser is a fun, innovative and informative Augmented Reality ( AR ) platform allowing you to discover what’s around you in a completely new way. By using the camera, simply hold up your smartphone and explore your surroundings.
Transparent, Modular Code Delivered Through Open Source Complete access to the computer vision algorithm allows you to modify the source code to fit your specific application. Freely distributed for use under a LGPL v3.0 license.
A more powerful way to engage, leading global brands use the Vuforia mobile vision platform to deliver unique, entertaining and interactive mobile experiences that transform the way users see and use brand apps.