Awesome C

A curated list of C good stuff. I give preference to free software for code, and sellers who aren't evil for physical resources.

This is released under the GNU Free Documentation License - its text is provided in the LICENSE file.

Compilers

• Clang - A C compiler for LLVM. Supports C11. NCSA.
• GCC - Provides a C compiler as part of its compiler set. Supports C11 and OpenMP. GNU GPL3.
• LCC - A Retargetable Compiler for ANSI C. Nonfree (but liberal) license. License.
• PCC - A very old C compiler. Supports C99. Various licenses
• TCC - Tiny C Compiler; a small, fast C compiler. Supports C99 (except complex types). GNU GPL2.1.

Crypto

• libgcrypt - A general-purpose cryptography library, with a range of available ciphers. GNU GPL2.1 and GNU LGPL2.1.

Database

This lists databases and data stores with C APIs.

• LMDB - An ultra-fast, ultra-compact key-value embedded data store. newOpenLDAP.
• MariaDB - A robust, scalable and reliable SQL server, designed to be a drop-in replacement for MySQL. 3-clause BSD.
• PostgreSQL - A powerful object-relational database system. PostgreSQL licence
• Redis - An advanced key-value store. 3-clause BSD.
• SQLite - A self-contained, serverless, zero-configuration, transactional SQL database engine with a C interface. Public domain.
• UnQLite - A self-contained, serverless, zero-configuration, transactional NoSQL engine with a C interface. FreeBSD.

Editors

These are specifically fancier, IDE-type editors. If you want a programmer's text editor, and yours doesn't support C, I'd be quite surprised.

• Anjuta DevStudio - The GNOME IDE. GNU GPL3.
• CodeLite - A cross-platform IDE. GNU GPL2.1.
• Geany - A very small and fast IDE. GNU GPL2.1.
• KDevelop - The KDE IDE. GNU GPL2.1.

Frameworks

This section has big libraries that provide data structures and other stuff you expect of a 'modern' standard library.

• APR - Apache Portable Runtime; another library of cross-platform utility functions. Apache2.0.
• C Algorithms - A collection of common algorithms and data structures for C. ISC.
• EFL - A large collection of useful data structures and functions. Various licenses, all free.
• GLib - A library of utility functions and structures, designed to be portable, efficient and powerful. GNU LGPL3.
• GIO - A modern and easy-to-use VFS API. GNU LGPL3.
• GObject - An object-oriented system and object model for C. GNU LGPL3.
• libnih - A lightweight library of C functions and structures. GNU GPL2.1.
• libU - A small library of basic utilities, including memory allocation, string manipulation and logging. 3-clause BSD.
• stb - A range of single-file libraries for C. Public domain.

Game Programming

• Allegro - A cross-platform, video game development and multimedia library. zlib.
• Corange - A game engine in pure C. FreeBSD.
• CSFML - A binding for SFML in C. zlib.
• FreeGLUT - An alternative to the OpenGL Utility Toolkit. Allows the creation and management of windows with OpenGL contexts. X11.
• GLFW - A multi-platform library for creating windows with OpenGL contexts. zlib.
• ioquake3 - The Quake3 engine, freed at last. GNU GPL2.1
• SDL - A cross-platform library designed to provide low-level access to audio, keyboard, mouse, joystick and graphics hardware via OpenGL. zlib.

Generic Programming

• klib - Small and lightweight implementations of common algorithms and data structures. Expat.
• SGLIB - Simple Generic Library; an implementation of a range of generic programming structures and idioms in C. GNU GPL3.

Graphics

• Cogl - A GPU graphics and utilities API. GNU LGPL2.1.
• Clutter - A UI library based on OpenGL. GNU LGPL2.1.
• OpenGL - The industry standard for high-performance graphics, with a native C binding. Various licenses.
• SDL2 zlib

Graphical User Interface

These are specifically widget toolkits.

• Elementary - A widget toolkit. Part of the EFL. GNU LGPL2.1.
• GTK+ - A cross-platform widget toolkit. GNU LGPL2.1.
• IUP - Another cross-platform widget toolkit. Expat.
• Tk - A basic widget toolkit. Part of Tcl/Tk. Tcl/Tk License.
• XForms Toolkit - A widget toolkit designed for the XWindow system. GNU LGPL2.1.

JSON

• Jannson - A C library for encoding, decoding and manipulating JSON. Expat.
• jsmn - A minimalistic JSON parser. Expat.
• WJElement - Advanced JSON manipulation library, with support for JSON Schema. GNU GPL3.
• YAJL - A fast C JSON streaming parser library. ISC

Learning and Tutorials

This is a list of resources for learning C programming in general, or something useful relating to C programming.

Online

• Bit twiddling hacks
• The C Programming Language 2E (online PDF)
• The lost art of C structure packing
• Writing efficient C and C code optimization

Physical

• 21st Century C - A very good second programming book on C.
• C Programming: A Modern Approach - An excellent book to learn the basics from C from.
• Expert C Programming: Deep C Secrets - An interesting, in-depth and entertaining look at the innards of C.
• Head First C - A 'head-first' style book for learning C.
• Understanding and Using C Pointers - An in-depth resource on pointers in C.

Multimedia

• FFMPEG - A complete, cross-platform solution to record, convert and stream audio and video. GNU LGPL2.1, with some parts under GNU GPL2.1.
• GStreamer - A framework for audio and visual media. GNU LGPL2.1.
• lodepng - A simple PNG image decoder and encoder, requiring no other dependencies. 3-clause BSD.

Networking and Internet

• asnlc - A compiler of ASN.1 specifications into C source code. FreeBSD.
• GnuTLS - A secure communication library, implementing SSL, TLS and DTLS. GNU LGPL2.1
• libcurl - A client-side URL transfer library, supporting a wide range of formats. curl license
• libev - Yet another event loop. FreeBSD.
• libevent - An event loop replacement for network servers. 3-clause BSD.
• LibreSSL - A BSD fork of OpenSSL. Various licenses, all semi-free.
• nanomsg - A C-based implementation of ZeroMQ. Expat.
• OpenSSL - Implementation of the SSL and TLS protocols, and also includes a cryptography library. Dual Licensed under the OpenSSL License and the SSLeay License
• Tox - A communication platform, designed to be a Skype-killer. GNU GPL3.
• ZeroMQ - High-performance message passing networking library. Implemented in C++, but has a C interface. GNU LGPL3.

Numerical

• ATLAS - Automatically Tuned Linear Algebra Software. 3-clause BSD.
• BLAS - Basic Linear Algebra Subprograms; a set of routines that provide vector and matrix operations. BLAS license
• FFTW - The Fastest Fourier Transform in the West; a highly-optimized fast Fourier transform routine. GNU GPL2.1.
• GMP - GNU Multple Precision Arithmetic Library; a library for arbitrary-precision arithmetic. GNU GPL2.1 and GNU LGPL2.1.
• GSL - The GNU Scientific Library; a sophisticated numerical library. GNU GPL3.
• KISS FFT - A very simple fast Fourier transform library. 3-clause BSD.
• LAPACKE - A C interface to LAPACK. 3-clause BSD.
• Yeppp! - Very fast, SIMD-optimized mathematical library. 3-clause BSD.

Parallel Programming

• OpenMP - A set of C pragmas designed to allow for easy parallelization of code. Standard (licensing not applicable).
• pthreads - The POSIX thread library. Standard (no license applicable).
• TinyCThread - A portable, small implementation of the C11 threads API. zlib.

Regex

"Some people, when confronted with a problem, think 'I know, I'll use regular expressions'. Now they have two problems." - Jamie Zawinski.

• PCRE - An implementation of regexes identical to that of Perl 5. 3-clause BSD.
• SLRE - Super Light Regular Expression library; a very small implementation of a subset of Perl regex syntax. GNU GPL2.1.
• TRE - A POSIX-compliant, feature-full regex library. FreeBSD.
• T-Rex - Another tiny regex library. zlib.

Serialization

• c-capnproto - An implementation of the Cap'n Proto serialization protocol. Expat.
• libavro - A C implementation of the Avro data serialization system. Apache2.0.
• msgpackalt - A simple, light and fast binary serialization library. 3-clause BSD.
• protobuf-c - An implementation of Google Protocol Buffer in C. FreeBSD.
• xdr - External Data Representation; a standard for data serialization. Standard (no license applicable).

Source Code Collections

This contains collections of small source code. If you want something big and integrated, check the Frameworks section.

• CCAN - Modelled after Perl's CPAN, this is a big collection of C code that does stuff. The full list is here. Various licenses (all free software).
• clib - Something of a package manager for C. Comes with a bunch of libraries of its own. Expat.
• gnulib - A collection of common GNU code. GNU GPL3.

Standard Libraries

This contains standard C libraries.

• Bionic - Google's C standard library, developed for Android. 3-clause BSD
• dietlibc - A C standard library designed for the smallest possible binaries. GNU GPL2.1.
• glibc - The GNU C Library; an implementation of the C standard library. GNU LGPL3.
• musl - A standard C library, compatible with POSIX 2008 and C11. Designed for static linking. Expat.

Testing

• CHEAT - A very simple unit testing framework. FreeBSD.
• Check - A unit testing framework for C. GNU LGPL2.1.
• cmocka - A unit testing framework with support for mock objects. Apache2.0.
• CUnit - Another unit testing framework for C. GNU LGPL2.1.
• minunit - Minimal unit testing framework for C. Expat.

Text Editor Extensions

While practically any decent programmer's text editor supports C, there are some extensions that make it more pleasant. This is categorized by editor.

Emacs

• Flycheck - Modern syntax checking. For C, it can use either GCC or Clang as a back-end. GNU GPL3.
• Yasnippet - A template system, with C templates for common code snippets. No license specified.

Vim

• YouCompleteMe - A code completion engine for Vim. GNU GPL3.

Tools

This is a list of useful programs to help you write and debug C code which are not editors, libraries or compilers.

• aimake - A build tool designed to avoid complex configurations. GNU GPL3.
• c99sh - Run C files using hash-bang. FreeBSD.
• GDB - The GNU Project debugger; a debugger for C. GNU GPL3.
• gprof - A performance analysis tool. Part of GNU binutils. GNU GPL3.
• rr - A debugger that records non-deterministic executions to allow for deterministic debugging. FreeBSD.
• Valgrind - A range of dynamic analysis tools, including a leak checker. GNU GPL2.1.

Utilities

This is a 'catch-all' category for anything that doesn't fit well anywhere else.

• bstrlib - The Better String Library. 3-clause BSD or GNU GPL2.1.
• Hans Boehm GC - Garbage collection for C? Don't mind if I do! Various licenses, all free.
• ICU - International Components for Unicode; a library for Unicode support. ICU license.
• libCello - A library introducing higher-level programming to C. 3-clause BSD.
• libffi - A portable foreign-function interface library. Expat.
• libgit2 - Pure C implementation of Git. GNU GPL2 with a linking exception.
• libPhenom - An eventing framework for building high-scalability and high-performance systems. Apache2.0.
• libuv - Cross-platform asynchronous I/O. Expat.
• Ragel - A DSL for state machines that compiles to C. GNU GPL3.
• SDS - Simple Dynamic Strings; a library for handling C strings in a simpler way, but one that is compatible with normal C string functions. Available via clib. FreeBSD.
• uthash - A hash table implementation, allowing existing structures to be stored in a hash table easily. 1-clause BSD

XML

"XML is crap. Really. There are no excuses. XML is nasty to parse for humans, and it's a disaster to parse even for computers. There's just no reason for that horrible crap to exist." - Linus Torvalds

• Expat - A stream-oriented XML parser. Expat.
• libxml2 - A standards-compliant, portable XML parser. Expat.