Ridetech offers the 4 link rear suspension in a parallel style. Very similar in construction to the tri link...rubber bushings, heavy tubing, lasercut bracketry...but the parallel 4 link uses a panhard bar to position the rear axle side to side.
In many applications, such as late model trucks, this configuration avoids interference between the upper bars and the oem gas tank. The parallel 4 link is also slightly easier for the casual installer to visualize and install because there are fewer bar mounts to deal with...the frame brackets and axle brackets carry both upper and lower bars. The parallel 4Link is available separately, with airsprings and weld-on bracketry, with bolt-on rear mounted airspring brackets, or with ShockWaves®.