BIMx is a mobile app for Building Information Modeling, provided by GRAPHISOFT. It aims to bridge the gap between the design studio and the construction site, by providing integrated 2D and 3D building project navigation with data access from any device.
Direct publishing to a 3D model can be done with a few other tools, but if (and only if) you are using ARCHICAD, it is the easiest to use. For Revit users, there is more choice, including Revit Live or some online model-viewers and publishers.
As an ARCHICAD user, this is almost a no-brainer. BIMx is included (although there are some paying options) and works well out-of-the-box. There is little to setup from the ARCHICAD side. You prepare a set of layouts/views and can publish the model on Ine go. The free version focuses on the 3D-model viewer. You publish an interactive model and can walk through it. With the PRO version, you also can publish the "Hyper-Model" - an integration of 2D and 3D views. If you are looking at tuning your own interactivity, e.g. in precisely defining what can happen and what information to show, you cannot customize BIMx that way. You have to look at alternatives, such as game engines or other 3D visualization software.
Most people using it are thrilled about it. But our use of ARCHICAD in projects is (alas) a bit limited, especially compared with the attention for Revit with our clients. And as an ARCHICAD teacher, I have to remember to keep introducing it as it is accepted well with most users.
Direct publishing to a 3D model can be done with a few other tools, but if (and only if) you are using ARCHICAD, it is the easiest to use. For Revit users, there is more choice, including Revit Live or some online model-viewers and publishers. For full custom interactivity, you have to look at e.g. Unity3D or Unreal where you can include and extend endlessly, but you will lack the ease of BIMx. You'd also have to look for good similar navigation. Especially the link between 2D views and 3D model sections is hard to beat. But in that context, if you want to e.g. allow users to choose design alternatives, select another material or include animations and sound, this is not possible in BIMx.