An exercise apparatus comprises a frame having two parallel tracks, two platforms mounted on the first track by a sliding bearing, and two platforms mounted on the second track by a sliding bearing. The tracks are spaced apart a sufficient distance to permit the platforms on different tracks to move freely past each other. A transverse interlock allows selective connection of platforms on different tracks for movement together and a longitudinal interlock allows selective connection of platforms on the same track for movement together. The frame includes cross braces connecting the rails at their ends, and the rails, cross braces, and platforms all include connecting points for permitting the user to selectively connect to and between the frame and the platforms a variety of exercise accessories or appliances. The accessories can include elastic resistance bands, cord and pulley assemblies, handles, weights, and appliances for administering physical therapy.