currently, there is no demo/test environment accessible and we are closing the beta next week. Starting early August, you will be able to obtain the MindDeveloper. With the MindAccess Developer package, you can send productive data into your own Tenant on MindSphere and use MindSphere standard applications (i.e. Fleet Manager) as well as develope own applications based on the data. You can also give access to these applications for productive usage to internal and external users.
As soon as the MindDeveloper is officially available, you will find more information here and on the blog.