Factor is a general purpose, dynamically typed, stack-based programming language released under a BSD-style license.
You can read about Factor's features and then download Factor. Factor runs on all of the most common platforms; see the download page for a full list.
Factor began life in 2003. Originally a scripting language for a Java game project and quickly grew into a general-purpose language. In mid-2004, a decision was made to write a native Factor implementation with a minimal core in C. The native implementation was bootstrapped from Java Factor, and soon thereafter native Factor became the de facto implementation. Work on the Java implementation stopped in late 2004.
Factor is very young and undergoing rapid development, however the stability, performance and completeness of the library is always improving, and a 1.0 release will be delivered some time in 2008.
Factor is used by approximately two dozen people world-wide. At any given time there are about six regular contributors. A core team of three developers, led by Slava Pestov, works on Factor full-time.