The Atreus is a portable ergonomic 40% keyboard sold as a kit.
It features a single-piece design with each hand's keys angled separately. Rather than the conventional row-staggering, the keys are arranged in column-staggering like the ErgoDox, which it is intended to complement. As a travel board, it measures 26x12cm and weighs about 300g. At the time of this writing, kits were offered with a choice of Matias switch (quiet clicks) or Cherry MX Blue.
The case has four layers, (3mm top layer, 3mm switch plate, 5-6mm spacer, and 3mm bottom layer) laser cut from either wood or acrylic. The construction uses a PCB with an A-Star Micro controller (with an AtMega32u4 chip) mounted onto it. There are 40 1x keys and two 1.5x keys in the middle for the thumbs.
The canonical case design is a couple EPS files, and there is a programmatically-generated OpenSCAD design that can be recompiled after tweaking the angles, row spacing, number of rows/columns, etc. Alternate case designs must be hand-wired.
The assembly guide steps through the construction process with instructions and photos.
The modifiers typically feature linear switches even when the rest of the keyboard is tactile because they are meant to be held instead of tapped, so they do not benefit from the tactile response.
The base layer contains all the alpha keys that are normally on rows 1-3. The fn layer contains most of the punctuation and the digits in a numpad design. A third layer contains arrows and function keys.
The design (case, PCB, and firmware) is licensed under the GNU General Public License version 3.