In helicopter, chod and running systems the rig is not fixed next to the lead but spins or slides along the leader. These set-ups excel over soft silt and weed and when casting at range. The group covers components and complete kits.
On a helicopter set-up the lead sits at the end of the leader and the rig spins around it between two beads. On the cast the rig flies behind the lead, so it does not tangle, which makes it very reliable at range.
On a chod system the rig slides freely on the leader and rides up over soft bottoms. With a running rig the lead slides on the main line, so the fish does not feel resistance straight away.
Safety is crucial: the top bead or stop must be able to pull off the end of the leader if the line breaks. Check that every component suits the diameter of your leader.