F83 implements an assembler, a memory hex dumper, an interpreter, a sort of bytecode compiler, a decompiler, a single-stepping source-level debugger, a screen editor (which could jump to the definition of any function and jump back and forth between source and documentation, and which tagged each screen of source code with the last edit date and author's initials), cooperative multitasking with thread-local data, a print spooler, and virtual memory. It can also compile programs into standalone executables, and in fact it's written in itself, so it can cross-compile itself for other architectures and operating systems; it supported CP/M-86, MS-DOS, and CP/M for the 68000.

The Forth programming language it implements is low-level but relatively powerful; among other things, it includes structured control flow, Turing-complete compile-time macros, closures, pointers, and multiple return values.

This is nothing unusual for a Lisp system, of course. What is different is that F83 is only about 2100 lines of code by my count. That's what makes it "more moldable" than a Lisp system with the same features, which would require around an order of magnitude more code.

There are some major compromises made in pursuit of this level of minimality, though: no type-safety (not even to the extent of calling functions with the right number of arguments), no built-in structs (though you can build them with its macro system and closures), no bounds-checking on arrays, error-prone manual access to the virtual-memory system, no syntax, no stack-allocated named variables, etc.