Ghostscript is a processor for PostScript and PDF files. It can rasterize these files to a wide variety of printers, devices for screen preview, and image file formats. Since applications tend to prepare pages for printing in a high-level format such as PostScript, most Unix users with low-level bitmap printers, such as inkjets, use GhostScript as part of the printing process. In addition, Ghostscript is capable of converting PostScript files, functionality comparable to Adobe Acrobat Distiller, but on the command line. In addition, Ghostscript is used for file import and viewing by a great many other applications, including xv, ImageMagick, gimp, and xdvi. Several GUI wrappers for viewing PostScript and PDF files exist, including GSview, ghostview, gv, ggv, and kghostview. This is far from a comprehensive list.
Ficl (Forth inspired command language) is an ANS Forth interpreter written in C. Unlike traditional Forths, this interpreter is designed to be embedded into other systems as a command/macro/development prototype language. Ficl provides object extensions that can be used to wrap methods and structures of the host system without altering them.
Lua is a programming language originally designed for extending applications, but also frequently used as a general-purpose, stand-alone language. It combines simple procedural syntax (similar to Pascal) with powerful data description constructs based on associative arrays and extensible semantics. It is dynamically typed, interpreted from bytecodes, and has automatic memory management, making it ideal for configuration, scripting, and rapid prototyping. It is implemented as a small library of C functions, written in ANSI C, and compiles unmodified in all known platforms. The implementation goals are simplicity, efficiency, portability, and low embedding cost. It has been used on games such as World of Warcraft, FarCry and Angry Birds, among others.
The Portable Forth Environment implements the ANSI Standard of the Forth programming language. It is fully written in C, and with gcc the virtual machine can be put into cpu registers. The newer development versions implement a set of modern features including modularization and multithreading. The terminal connection itself can be configured to work in an embedded environment.
Python is an interpreted, interactive, object-oriented programming language. It combines remarkable power with very clear syntax, and isn't difficult to learn. It has modules, classes, exceptions, very high level data types, and dynamic typing. There are interfaces to many system calls and libraries, as well as to various windowing systems (Tk, Mac, MFC, GTK+, Qt, wxWindows). New built-in modules are easily written in C or C++. Python is also usable as an extension language for applications that need a programmable interface.
TinyScheme is a lightweight Scheme interpreter that implements as large a subset of R5RS as possible without getting very large and complicated. It is meant to be used as an embedded scripting interpreter for other programs. As such, it does not offer IDEs or extensive toolkits although it does sport a small top-level loop, included conditionally. A lot of functionality in TinyScheme is included conditionally, and it allows multiple interpreter states to coexist in the same program without any interference between them. Foreign functions in C can also be added and values can be defined in the Scheme environment.
SmallBASIC is a free interpreter for BASIC, a simple computer language, targeting simplicity, mathematics, and graphics. Also, it has a powerfull string library, supports external C modules (shared libs), uses dynamic arrays (by default) and has no data types. Versions exists for Linux (or other Unix), PalmOS, DOS, Win32, VTOS (Helio), and Franklins (eBookman). It uses a lot of drivers, including svgalib, ncurses, and framebuffer.