There’s also Maru that is worth mentioning when it comes to API frameworks written in Elixir. Seems to be actively maintained.
But, given you are new to Elixir, I would consider Phoenix as there’s far more resources on it than anything else out there. When you get stuck, help will be far more within your reach.
It’s the first time I hear about Rackla, thus I can’t comment on its viability.
