The Kastenwagen 1840, designed and shared by Alex Ronke aka NoPunIn10Did, is a 40% board with a 13.75u long alpha block, exploded arrow keys, LED layer indicators, and a mini-numpad. The 48 replaces the numpad with a macro column.
The Kastenwagen 48 is a similar keyboard that replaces the mini-numpad with a small macro column.
Last year, I ran a limited prototype run for two related keyboards: the Kastenwagen 1840 and the Kastenwagen 48. This was a fun board to design and build, but apart from a handful of dedicated users, it has been largely forgotten – NoPunIn10Did.
Part of this, the author suspects, is that the design of the main alpha portion of the board was specifically made with non-US alphas in mind (particularly German or Nordic). The 11 alpha columns in the Q and A rows leave enough space for the additional non-English letters like Ü, Ö, Ä, Å, Ø, and Æ.
The current design of the board assumes an Elite C as its microcontroller / daughterboard (NOT a Pro Micro).