CGUI - Library for making GUIs in a simple way.
Curses - Standardized console user interface library.
GTK+ - Cross-platform Graphical User Interface Library.
IUP - Portable toolkit for building graphical user interfaces.
wxC - Cross-platform Graphical User Interface Library.
Windows API - Windows GUIs and more
X11 - Windowing system commonly used on Linux systems

Allegro - Game programming library.
DUGL - Game and graphics library for DOS.
caca - A colour ASCII art library.
Cairo - 2D graphics library with support for multiple output devices.
DISLIN - Library of subroutines and functions that display data graphically.
freeglut - A free alternative to GLUT, an OpenGL library for window creation and callback-based input handling
FreeImage - Open Source library to support popular graphics image formats.
Freetype2 - A Free, High-Quality, and Portable Font Engine.
GD - Open source code library for the dynamic creation of images by programmers.
GIFLIB - Portable tools and library routines for working with GIF images.
GLUT - the original (but now inactive) OpenGL Utility Toolkit
GLFW - An OpenGL library for creating an OpenGL window and handling input from the user's main loop
GRX - 2D graphics library.
IL (DevIL) - A full featured cross-platform image library.
japi - Open source free software GUI toolkit using Java's AWT Toolkit.
jpeglib - Cross-platform library for reading/writing jpeg images.
JPGalleg - A small add-on for Allegro that adds JPG images handling capabilities to the library.
libpng - Allows reading and writing PNG images.
OpenGL - Cross-platform 3D Graphics library.
PDFlib - Portable library for dynamically generating PDF documents.
SDL - Cross-platform multimedia library.
TinyPTC - A small and easy to use framebuffer graphics library.

BASS - Audio library for use in Windows with a beta for Linux.
BASSMOD - BASSMOD is a MOD only (XM, IT, S3M, MOD, MTM, UMX) version of BASS
Flite - Run time speech synthesis engine
FMOD - Audio library supporting just about any format.
MediaInfo - Library to read out technical and tag information from many media file formats
mpg123 - MPEG (including MP3) decoder library
Ogg - Ogg multimedia container format creation/decoder library
OpenAL - Cross-platform 3D audio API.
PortAudio - Cross-platform audio I/O library
sndfile - Library to read/write/convert audio files in various formats
VLC - Audio/video playback
Vorbis - Ogg Vorbis audio compression library

GDBM - Database functions using extensible hashing, primarily for storing key/data pairs to data files
MySQL - High-Quality, widely used database engine.
PostgreSQL - Free software object-relational database management system
SQLite - Small C library that implements a self-contained, embeddable, zero-configuration SQL database engine.

CUnit - Lightweight system for writing, administering, and running unit tests in C.
GDSL - The Generic Data Structures Library is a collection of routines for generic data structures.
gettext (includes libintl) - Internationalization mechanism
GNU ASpell - Free and Open Source spell checker.
libbfd - Allows applications to use the same routines to operate on object files whatever the object file format.

JNI - Standard programming interface for writing Java native methods and embedding the Java virtual machine into native applications.
json-c - A JSON implementation in C
libffi - Foreign function interface and closure library
libjit - Runtime (just in time) compilation library
Lua - Lightweight, embeddable scripting engine using the Lua language.
SpiderMonkey - Embeddable javascript engine.

cryptlib - A powerful security toolkit which allows even inexperienced crypto programmers to easily add encryption and authentication services to their software.
UUID - Universally Unique Identifier generation and parsing library

big_int - Library for using arbitrarily large integers.
Chipmunk - 2D rigid body physics library
GMP - Free library for arbitrary precision arithmetic, operating on signed integers, rational numbers, and floating point numbers.
GSL - Provides a wide range of mathematical routines such as random number generators, special functions and least-squares fitting.
Newton - Integrated solution for real time simulation of physics environments.
ODE - Open source, high performance library for simulating rigid body dynamics.

cgi-util - Small C library for creating CGI programs for Websites.
curl - Free and easy-to-use client-side URL transfer library supporting almost every protocol.
FastCGI - Open extension to CGI that provides high performance without the limitations of server specific APIs.
ZeroMQ - High-performance asynchronous messaging library

Expat - Stream oriented XML parser library with several useful features.
libxml - De-facto standard library for accessing xml files.
libxslt - XSLT itself is a an XML language to define transformation for XML.
Mini-XML - Small XML parsing library that you can use to read XML and XML-like data files in your application.

PCRE - Regular expression pattern matching using the same syntax as Perl.
TRE - Lightweight, robust, and efficient POSIX compliant regexp matching library.

bzip2 - For reading/writing .bz2 files or in-memory (de)compression using the bzip2 algorithms
libzip - Easy-to-use library for creating and unpacking .zip files
liblzma - Strong LZMA-based compression library used for .lzma and .xz file formats
LZO - Offers fast compression and very fast decompression.
QuickLZ - Very fast Compression Library
zlib - Lossless data compression library unencumbered by patents.

C Runtime Library
DOS API
disphelper - Helper library to use COM objects from plain C
GLib - GNOME's universal cross-platform software utility library
Windows API
X11 - Windowing system commonly used on Linux systems

Visit http://www.freebasic.net/___old_site/arch/ for other libraries.