LuaZ80 is a Open Source project (by me) that emulates a Z80 microprocessor in Lua. However, it's not just a simple read-decode-execute loop of normal emulators, but a dynamic translator that changes Z80 machine code into Lua code then executes that Lua code. This is sort of like a JIT compiler that translates Z80 into Lua.
It's a work in progress and a proof-of-concept project.
More information can be found at it's github page here: http://github.com/robzed/LuaZ80.
Z80 chip image adapted from http://commons.wikimedia.org Zilog_Z80.jpg by Gennadiy Shvets. Lua logo Copyright © 1998 Lua.org.
As far as I know, it's the first Lua Z80 dynamic translator, and possibly the first Z80 Lua emulator (incomplete as it is...).
The closest thing to a Z80 emulator (in Lua) is the Game Boy processor emulator inside Garryboy which is a Game Boy emulator for Garry's Mod. The Game Boy processor isn't a Z80, but an 8080-derived processor with some Z80 instructions added (CB prefix) as well as unique auto-increment/decrement addressing modes (wikipedia).
Other dynamic-translation emulators written in dynamic-programming-languages
Everyone should visit jslinux and read the FAQ and Technical notes. LuaZ80 doesn't share actual technical ideas or code from jslinux, but the fact such a cool thing was possible, has obviously been an influence.