prod.ex

defmodule P do
  def product([]) do
    []
  end

  def product(lists) do
    product(lists, [])
  end

  def product([h|t], args) do
    Enum.map(h, fn x ->
      product(t, [x | args])
    end) |> Enum.concat
  end

  def product([], args) do
    [list_to_tuple(Enum.reverse(args))]
  end
end

prod_test.ex

iex(7)> P.product([[0, 1]])
[{0}, {1}]

iex(8)> P.product([[0, 1], [:a, :b]])
[{0, :a}, {0, :b}, {1, :a}, {1, :b}]

iex(9)> P.product([[0, 1], [:a, :b], ['x', 'y']])
[{0, :a, 'x'}, {0, :a, 'y'}, {0, :b, 'x'}, {0, :b, 'y'}, {1, :a, 'x'},
 {1, :a, 'y'}, {1, :b, 'x'}, {1, :b, 'y'}]