Mechanical metamaterials are architected structures designed to exhibit unconventional mechanical responses. Their engineered properties make them especially valuable for realizing precise motion and load-bearing functions, with broad applications in machines, robotics, and related technologies. Straight-line mechanisms, typically based on compliant or rigid designs, offer compactness and accuracy but are often limited by parasitic motion, restricted range of motion, and load-capacity constraints. In this work, we introduce the concept of shear cell, develop a suitable embodiment, and demonstrate how a planar straight-line metamaterial mechanism approximates its behavior. Both series and parallel tessellations of a rectangular shear cell are investigated, considering full and partial scaling strategies. Through analytical modeling, finite element simulations, and experimental validation, we examine how tessellation influences key performance parameters, including range of motion, stiffness, and crosstalk. Finally, the concept is extended to demonstrate the design of planar multi-degrees-of-freedom mechanisms and spatial straight-line metamaterial motion systems.