The plumber has connected all the radiant heat tubes for the basement floor. The tubes across the top (with the yellow valves) are the hot supply going out to the multiple (9) loops, which return to the bottom pipe. The green thing is the pump that runs this heat circuit, and to the left of that (partially obscured by the yellow valve handles) is a "mixing valve". The mixing valve sets the water temperature by mixing some ratio of hot water (from the upper pipe, from the boiler) with cooler water (from the lower pipe, returning from the floor loops).