By "freely available" do you mean "available for free"? If there is a free program, it probably isn't worth the cost.
Foregas has a gas lift module (not an inexpensive product), but I'm not real thrilled with the algorythm they are using for annular flow. Since Haliburton owns Pipesim, I'd expect that product to have something (but it is also not inexpensive). Weatherford has a program that they run internally, but I don't think it is for sale.