{scrletter} is for questions addressing issues related to the KOMA-Script letter package scrletter.
{scrletter} is part of KOMA-Script. This package provides the letter-based functionality of {scrlttr2} to the other KOMA-Script classes.
The current documentation can be found by typing texdoc KOMA-Script, then choose scrguien.pdf (English manual) or scrguide.pdf (German manual).
There is also an undocumented wrapper-class scrletter. It loads class scrartcl with font size 12pt and package scrletter.