The main repository of Lua modules is LuaRocks. See also Awesome Lua. Pre-compiled Lua libraries and executables are available at LuaBinaries. The lua-users wiki lists many user-contributed addons for Lua.
Lua is implemented in pure ANSI C and compiles unmodified in all platforms that have an ANSI C compiler. Lua also compiles cleanly as C++.
Lua is very easy to build and install. There are detailed instructions in the package but here is a simple terminal session that downloads the current release of Lua and builds it in Linux:
curl -L -R -O https://www.lua.org/ftp/lua-5.4.6.tar.gz tar zxf lua-5.4.6.tar.gz cd lua-5.4.6 make all test
If you have trouble building Lua, read the FAQ.
You can also help to spread the word about Lua by buying Lua products at Zazzle.