Programming language Refal, invented by ValentinTurchin.
Declarative (functional, applicative) language. No destructive assignment. Powerful pattern matching. Sequence as native datatype (has functionality of nested double-linked lists, not s-expressions). Proper tail-recursion.
Used for research on supercompilation (SuperCompiler).
Home page: http://www.refal.org/index_e.htm
Typical applications: transformation of tree-structured data (like e.g. XML documents, see http://www.refal.org/english/xmlref_1.htm)
Refal implementors (run-time system, development tools, libraries, documentation):