This paper provides an overview of a real-time multi-user multiple-input multiple-output (MIMO) communication testbed designed for demonstration and assessment of real-world wireless communication aspects. The testbed is built on a modular hardware platform consisting of three different boards and incorporates a MIMO-OFDM-based physical (PHY) layer, an embedded media access controller (MAC), and an Ethernet interface. Due to the modular design of the testbed, it can be used for both, real-time and offline processing experiments with real-world aspects.