Please note that most developers prefer to only bind to the few library calls they actually need. E.g. an rmdir() binding is just a single line with the LuaJIT FFI. And a simple binding to e.g. zlib takes only two dozen lines, see the FFI Tutorial. You can find many examples for this floating around on the net.

The following list only shows larger or somewhat comprehensive library bindings:

Core OS Libraries

• ljsyscall: Linux system calls.
• luapower/winapi: Win32 API
• luapower/objc: Objective-C & Cocoa bridge
• luapower/pthread: POSIX threads (Linux/OSX/Winpthreads portable subset)
• luapower/time: time, clock, sleep (Linux/OSX/Windows)
• LJIT2Win32: Core Windows libraries.
• ljf-com: Microsoft COM.
• LJIT2RPi: VideoCore of Raspberry Pi.
• TINN: Windows API Sets, includes a shell.
• lua-resty-fileinfo: libmagic.

Databases

• luajit-mysql: MySQL.
• luapower/mysql: MySQL.
• LJIT2Sophia: Sophia.
• lsqlite3-ffi: SQLite.
• LJIT2SQLite: SQLite.
• LJSQLite3: SQLite3.
• mongolua: MongoDB and BSON library.
• luajit-unqlite: UnQLite.

Graphics

• glua: OpenGL/GLUT.
• LuaJIT-GLFW: OpenGL and GLFW.
• luajit-glfw: GLFW v3.1.1-v3.2.0.
• LJIT2Khronos: Khronos (OpenGL, EGL, OpenCL, OpenVG)
• luapower/cairo: cairo graphics library.
• luapower/clipper: clipper (polygon clipping).
• luapower/giflib: giflib.
• luapower/nanojpeg: nanojpeg.
• luapower/libjpeg: libjpeg. Comes with libjpeg-turbo binaries.
• luapower/freetype: freetype.
• wklua: wkhtmltopdf.
• LuaJIT-SDL2: SDL2 with threads and audio.

Audio & Video

• openal-lua-ffi: OpenAL.
• wavpack-lua-ffi: Wavpack.
• libsndfile-lua-ffi: libsndfile.
• mad-lua-ffi: MAD (MPEG Audio Decoder).
• ffmpeg-lua-ffi: ffmpeg.
• LJIT2X264: X264

Messaging & Events

• lua-zmq: ZeroMQ.
• lzmq: ZeroMQ.
• libev: libev.
• fend: epoll.
• epoll_ffi: epoll.
• ffi_libmosquitto: libmosquitto (MQTT client library).

Networking

• luajit-ffi-enet: Enet.

Encoding & Decoding

• luajit-msgpack-pure: MessagePack.
• iconv-lua-ffi: iconv.
• LJIT2Http_Parser: HTTP parser.
• luapower/expat: expat XML parser.
• luapower/genx: genx XML generator.
• lua-resty-libcjson: (cJSON) JSON encoder / decoder.
• lua-resty-hoedown: Markdown and SmartyPants parser.

Crypto

• lua-libssh: libssh (OpenSSH).
• LJIT2WinCNG: WinCNG.
• luapower/md5: MD5.
• luapower/sha2: SHA-256, SHA-384, SHA-512.
• lua-resty-scrypt: Scrypt (password) hashing.
• lua-bcrypt: LuaJIT FFI binding for OpenBSD bcrypt (only usable on OpenBSD)

Compression

• luapower/zlib: zlib.
• luapower/minizip: minizip.
• lua-resty-snappy: snappy.
• ljlz4: lz4.

Game Engines

• allua: Allegro 5.

Cross-language RPC

• Motan-OpenResty: A cross-language RPC framework.

Cross-language Bridges

• TLC (Tiny Lua Cocoa bridge): Objective-C bridge.

Unicode

• luapower/libunibreak: Unicode line breaking and word breaking.

Miscellaneous

• ufo: Precompiled binaries for OSX/Windows and other platforms. Bindings for: Cairo, Pixman, SDL 1.3, zlib, libpng, libbz2, ZeroMQ, Expat, Freetype, GLFW, APR, AntTweakBar, OpenGL, OpenCL.
• luapower/hunspell: hunspell (spell checking)
• luajit-tcc: Tiny C Compiler.
• luapower/luastate: binding to the Lua C API for creating independent Lua states
• luapower/dynasm: use DynASM from Lua
• luapower/cbframe: low-level FFI callback frames (workaround to FFI ABI limitations)
• luajit-gmp: GNU Multiple Precision library.
• lua-clang: Bindings for C Interface to Clang.