Network slicing represents a new paradigm to operate mobile networks. With network slicing, the underlying infrastructure is ``sliced” into logically separate networks that can be customized to the specific needs of their tenant. Hands-on experiments on this technology are essential to understand its benefits and limits, and to validate the design and deployment choices. While some network slicing prototypes have been built for RANs, leveraging on the wide availability of radio hardware and open source software, there is currently no open source suite for end-to-end network slicing available to the research community. In this article we fill this gap by developing an end-to-end network slicing protocol stack, POSENS, which relies on a slice-aware shared RAN solution. We design the required algorithms and protocols, and provide a full implementation leveraging on state-of-the-art software components. We validate the effectiveness of POSENS in achieving tenant isolation and network slices customization, showing that no price in performance is paid toward this end. We believe that our tool will prove very useful to researchers and practitioners working on this novel architectural paradigm.