Many of the branches here are out of date. The clojure koans have moved on to functional-koans/clojure-koans, the F# koans have moved on to ChrisMarinos/FSharpKoans and the scala koans have moved over to bitbucket. Please feel free to browse here but I suggest you look to the other places for more current code.
There are several functional languages that have contributed their own versions of the koans. Each language has it's own branch with detailed instructions on how to get started.
To get the koans for a particular language, simply checkout the branch:
git checkout -b <branch_name>
where is the name of the branch (language) you want to work on. To get a list of all branches run:
git branch -a