Nyarna has been developed as research project at the Institute of Software Engineering, University of Stuttgart, Germany.
The tour is the current authoritative source for the language syntax and semantics. A proper specification has been written during the course of the language's development, but is not up-to-date and would therefore not be of any use. The plan is to release it after a proper rewrite.
The reference implementation, as well as the content of this site, is licensed under the terms of the MIT license.
The reference implementation written in Zig is publicly available here. It is in no way stable and may crash on invalid and even valid input.
The standard library is almost non-existing and a lot of simple functionality is missing. There is no proper release yet, partly because development follows Zig's master branch and the implementation's code doesn't build with any released Zig version. The interactive interface in the tour is currently the best way to try out the language.