Tcl provides a portable scripting environment for Unix, Windows, and Macintosh that supports string processing and pattern matching, native file system access, shell-like control over other programs, TCP/IP networking, timers, and event-driven I/O. Tcl has traditional programming constructs like variables, loops, procedures, namespaces, error handling, script packages, and dynamic loading of DLLs. Tk provides portable GUIs on UNIX, Windows, and Macintosh. A powerful widget set and the concise scripting interface to Tk make it a breeze to develop sophisticated user interfaces.
Onyx is a powerful stack-based, multi-threaded, interpreted, general purpose programming language similar to PostScript and Forth. It can be embedded as an extension language into other applications, and was designed to have a small memory footprint. It is among the smallest embeddable interpreters available.
uIP is probably the smallest implementation of the TCP/IP protocol stack ever written in a high level language; the code footprint is on the order of a few kilobytes and RAM usage is on the order of a few hundred bytes. uIP is intended to be used in embedded systems running low end 8- and 16-bit microcontrollers.
Contiki is an open source, highly portable, networked, multi-tasking operating system for the Internet of Things. Contiki includes a multitasking kernel, a TCP/IP stack and a set of application programs, and a low-power radio communication stack. It is written in C and designed to be very small: it runs comfortably in a few kilobytes of RAM.
Hedgehog is a very concise implementation of a Lisp-like language for low-end and embedded devices. It consists of a compiler and a byte code interpreter. The Lisp dialect has proper support for local and lambda functions, lexical scoping, variable argument functions, garbage collection, exceptions, macros, and over a hundred predefined functions or special forms. The built-in types are lists, symbols, strings, 32-bit integers, AVL trees, and tuples up to 16 elements wide.
Protothreads are a type of extremely lightweight, stackless threads written in 100% portable C. While protothreads were originally designed for severely memory-constrained systems such as deeply embedded systems, they have found a number of uses as a general purpose portable library as well.