Aluminum window framing is often considered a step up from wood or vinyl windows as aluminum is strong, joins together simply, and is less vulnerable to moisture damage. Aluminum framing and mullion sections are extruded and provide crisp, aesthically pleasing profiles which come equipped with factory finishes. ALuminum does conduct heat rapidly however so a thermal break of plastic or synthetic rubber is typically utilized to eliminate thermal flow through which can cause fogging and also frost on the interior side during winter months. Aluminum windows are typically more expensive than wood or plastic but the cost is often justified from a maintenance/durability standpoint, especially in commercial applications.
The most common finish on aluminum windows is Anodized and the most common color choices are: clear, champagne, light bronze, medium bronze, dark bronze, and black. 
Baked enamel and fluoropolymer resins are available as well.
Frame depths most commonly range from 2″ to 4-1/2″ but custom sizes are available. Glass can be single, double, or triple paned, thermally insulated or not, with out low-e option.
          Aluminum is subject to galvanic action so any anchors or fasteners used must be aluminum, galvanized steel, stainless steel, or other compatible material. Also the rough opening must be flashed with a compatible material as well. Copper, concrete, and masonry should not be used in contact with aluminum windows, but can be coated with zinc-chromate primer, aluminum paint, or specialized bituminous coatings.
Thermally Broken Aluminum WIndow
Mortar, concrete, or plastic splashed onto aluminum window frames and left to dry can corrode the aluminum. Exposed aluminum can be protected with a clear lacquer, strippable coatings, or tapes. Concealed aluminum that will be in contact with or near concrete, masonry, insulation, or wood which might maintain high moisture, should be protected by coatings. After installation, aluminum windows are caulked at the perimeter/rough opening joint to weatherproof.  
          For the standard double-paned aluminum framed window, any sashes larger than +/- 50 square feet will require field glazing. Sashes under 50 square feet can typically be pre-assembled at the manufacturer (with exact rough opening measurements) or in the glaziers shop.