Title says it all.
The MastMate system is a long run of seat-belt material, with alternating "steps" made of loops of the same material sewn in place.
It is hoisted from your halyard and held in place next to your mast with mast slugs and plastic shackles (sorry, not included).
This sale includes only the MastMate itself.
$150 plus shipping, or $125 if you pick it up in Eastern Connecticut.