No food in the Poaceae family, or in any plant family, that is used like a grain.
Amaranth, Buckwheat, Teff, Rice for example are avoids.

Other 'Grain Eliminating diets' generally just refer to the Pooideae sub-family of grasses in Poaceae that includes Wheat: thus generally Millet, Rice, and Bamboo are safe, and Rye is always questionable.