There is one version Lua for the ESP8266 (and ESP32), that is still under active development and maintenance: NodeMCU Lua Firmware on GitHub with its online documentation set available here.
After initial closed source development by the NodeMCU hardware developers, they released the software project to open-source in October 2014, and soon after invited a core group of community contributors to take over the software project. This team has made some 1,800 material commits to the software base in the 3 years since the projects move to GitHub, with some 60 hardware and software modules now supported. For further details see the online documentation.
A second version of Lua know as NodeLua stopped development in December 2014, soon after NodeMCU Lua was open-sourced, and is now moribund, as it does not work with any of version 1.x or 2.x releases of the Espressif non-OS SDK.