DeKnit carriage unknits (unravels) stitches and rows of knitted fabric.
I owe one and just tried it to unravel several rows of my tuck-stitch pattern. Simple stockinet stitches unraveled quickly but my tuck stitched had problems. The manual only mentions specifics for weaving and fair isle stitches.
The DeKnit also comes in white.
The photos below show the DeKnit carriage, which I successfully used on Brother knitting machine.
There are different DeKnit carriages for different knitting machine models. They might look the same on the face-side but different on the undercarriage side.
Below are the carriages for Brother (on the left side, blue DeKnit) and Singer/Silver Reed/Studio (on the right-hand side, white deKnit) machines.
Notice, how they look almost the same. However, the way the undercarriage is designed is different: note the differences on the very top of the carriage. The main difference is how the DeKnit attaches to the main bed. Beds of Brother and Singer/SilverReed/Studio are slightly different.
A special thanks for one of my knitting-machine friends for providing the last two pictures and for answering questions about the DeKnit carriage. It takes a village!