Gforth is the GNU implementation of Forth, a stack-based low-level programming language. Documentation for Gforth is available at http://www.complang.tuwien.ac.at/forth/gforth/Docs-html/.
This image contains the latest version of Gforth compiled from source and includes support for the C foreign function interface and disassembly with GDB.
Gforth source files defining extra features are located in /usr/share/gforth/$GFORTH_VERSION. This directory is in Gforth's default search path, and so you just need to run, say, include random.fs to be able to use seed, rnd, and random.
Starting the image without any arguments puts you in interactive (REPL) mode, which is often what you want:
$ docker run -it jwodder/gforth
Alternatively, you can run a Forth script from your current directory as follows:
$ docker run -it -v "$PWD":/usr/src/myapp -w /usr/src/myapp jwodder/gforth gforth your-script.fs -e bye
Note that the -e bye at the end is needed to keep Gforth from entering interactive mode once the script completes.