Scheme 48 is a free software

Free software

Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

 Scheme implementation using a bytecode

Bytecode

Bytecode, also known as p-code , is a term which has been used to denote various forms of instruction sets designed for efficient execution by a software interpreter as well as being suitable for further compilation into machine code...

 interpreter. It has a foreign function interface

Foreign function interface

A foreign function interface is a mechanism by which a program written in one programming language can call routines or make use of services written in another. The term comes from the specification for Common Lisp, which explicitly refers to the language features for inter-language calls as...

 for calling functions

Subroutine

In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....

 from C

C (programming language)

C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

 and comes with a regex

Regular expression

In computing, a regular expression provides a concise and flexible means for "matching" strings of text, such as particular characters, words, or patterns of characters. Abbreviations for "regular expression" include "regex" and "regexp"...

 library, and a POSIX

POSIX

POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...

 interface. It is supported by SLIB

SLIB

SLIB is a Scheme library written by Aubrey Jaffer. It uses only standard syntax and consequently works on many different Scheme implementations, such as Bigloo, Chez Scheme, Extension Language Kit 3.0, Gambit 3.0, GNU Guile, JScheme, MIT/GNU Scheme, Pocket Scheme, Racket, RScheme, Scheme 48, SCM,...

 the portable Scheme library and is the basis for Scsh

Scsh

Scsh is a POSIX API layered on top of the Scheme programming language in a manner to make the most of Scheme's capability for scripting. It is limited to 32-bit platforms but there is a development version against the latest scheme48 that works in 64bit mode.....

, the Scheme shell.

It is called "Scheme 48" because the first version was written in 48 hours in August 1986.

The authors now say it is intended to be understood in 48 hours.