Shear tools are described that are driven by a power assembly. In one version, the shear tools include a pivotally movable pair of lever arms. Upon activation of the power tool, the lever arms of the shear tool are pivotally displaced and urge a die along a shearing plane relative to another stationary die retained by the shear tool. In another version, the shear tools include a carriage and link assembly. Upon engagement and activation with a power assembly or power tool, a movable die is urged past a stationary die. Also described are systems and related methods utilizing the shear tools which enable convenient shearing or severing of workpieces such as strut channel.