Fortress Anchors markets the Fortress aluminum-magnesium alloy anchor as the 'world's best anchor', according to many tests conducted around the world (and prior to the wide-spread realworld deployment of the new 3rd generation anchors such as the Spade and Roca).
The Fortress, and the less expensive, more utilitarian-finish, Guardian, anchors weigh half as much as steel. Fortress anchors rely on their design not their weight to perform.
Fortress anchors have an anodized finish, are completely able to be dissasembled (the company even sells durable Cordura soft cases to store them), have adjustable fluke angles (increased angle for use in mud and soft bottoms), are used by the US Navy and Coast Guard, are approved the American Bureau of Shipping and are made in the USA.
Manufacturer's website here: Fortress Anchors.
Invented by Don Hallerberg in 1992. The patent, number 5,154,133, and a drawing below as well, describes the Fortress as a "twin-fluke anchor, capable of disassembly, for mooring a marine vessel in waters having generally sandy or muddy underwater bottoms to prevent the vessel from drifting with the wind or tide. The anchor is capable of assembly in two different configurations to vary the shank/fluke angle to optimize the holding power of the anchor in accordance with the firmness of the underwater bottom surface." Hallerberg's previous patent, number 4,892,053 in 1990, shows virtually the same design but without the adjustable fluke angles.