Factor is a concatenative programming language by Slava Pestov. It is inspired by Forth, but includes garbage collection, dynamic typing, a modern object system and combinator words for expressing abstractions.
Factor code is compiled to x86 machine code by the Factor runtime. It supports Windows, Linux and Mac OS X platforms. The language features extensive metaprogramming capabilities, and large amounts of the language, including the object system and the native code generation, are implemented as libraries a programmer can manipulate if necessary.
The standard library includes a graphics/GUI toolkit which uses OpenGL. FFI to C is straightforward, and can be used to set up support for curses or libtcod. The library that comes with the language is comprehensive, and includes such gamedev-relevant features as vector and matrix arithmetic and A*-search.
The language has software-based cooperative threads, but no actual multiprocess support as of 2010-11.