From their website:
RETRO is a clean, elegant, and pragmatic dialect of Forth. It provides a simple alternative for those willing to make a break from legacy systems. The language draws influences from many sources including traditional Forth systems, cmForth, colorForth, Factor, and Parable. It was designed to be easy to grasp and adapt to specific uses. The basic language is very portable. It runs on a tiny virtual machine (Nga), which is written in C. There are multiple interface options, the main one (rre) is buildable with just the standard C compiler and libraries on most systems.
I am trying it out just to see what Forth is like!