CLISP is a portable ANSI Common Lisp implementation and development environment by Bruno Haible. Interpreter, compiler, debugger, CLOS, MOP, FFI, Unicode, sockets, CLX. UI in English, German, French, Spanish, Dutch, Russian, and Danish.
Mathfun.py is a Python library that contains those little bits of mathemagical ideas that we all enjoy. Primes, prime factorization, Fibonacci sequences, string2value functions...