The past decade has shown distinct advances in the theory of MIMO techniques for wireless communication systems. Now, the time has come to demonstrate this progress in terms of applications, where the intermediate step towards a customized product consists in more or less rapid “prototyping”. Due to the multitude of different algorithmic approaches, i.e. beamforming, space-time coding, spatial multiplexing, and of different standards, i.e. UMTS, WLAN's, an ideal prototyping platform requires a high degree of flexibility and modularity in order to be qualified for a wide range of potential applications. The aim of this contribution is to give an overview about the challenges, the rich variety and the usefulness of such MIMO hardware platforms.