An advanced letter document class which extends LaTeX's usual letter class, providing support for building your own letterhead and marking fold points for window envelopes. Options supported by the package include: letterpaper for US letter; a4offset for a modified A4 layout suitable for platic binders that cover a part of the left margin. Also includes isodate to set the date as YYYY-MM-DD as descibed in ISO 8601 and DIN 5008 and akfaxps a new configuration example that uses Times/Courier. The author is Axel Kielhorn. See also brief dinbrief envlab formlett.