Metal sill extensions, similar to what is typical in Sweden.
EAST FACADE. renovation of gyldenrisparken social housing, copenhagen. vandkunsten/witraz/wissenberg 2005-2012 (by seier+seier)
Interesting mix of wood and aluminum window frames
(via Wood European Windows | Wood European Doors | Bieber Architectural Windows) Passive House certified line, triple glazed, aluminum clad. Looks promising, but not made in the US.
PH certified, appears to be aluminum cladding over some kind of insulating material at the exterior, fir at the interior.
Danish made PH certified polymer framed windows: Ecliptica.
Interior frame material appears to be plastic shell filled with stone wool insulation.
Casagrande Woodworks - a new PH certified window product, made in the US
A new entry in the Passive House window race - from Ireland?
Full blown box bays, like for the whole building!
Interesting assemblage of window units to build a window wall.