LuaTeX is an extended version of pdfTeX using Lua as an embedded scripting language. The LuaTeX projects main objective is to provide an open and configurable variant of TeX while at the same time offering downward compatibility. From the user perspective we have pdfTeX as stable an more or less frozen 8 bit engine, XeTeX as unicode input and font aware engine using libraries for font handling, and LuaTeX as engine that is programmable and delegates as much as possible to Lua, with the objective to keep the core engine lean and mean. Each engine has it's benefits and drawbacks (more details here).
At the TUG 2007 conference in San Diego, the first public beta of LuaTeX was presented. Most of that day was dedicated to the project, its outcomes and its objectives (this project is partly driven by the oriental TeX project). Videos of the conference can be seen here.
There are three closely related projects:
The first two projects result in a collection of OpenType fonts that can be used in LuaTeX and XeTeX. The third project results in a MetaPost library (to be used in LuaTeX) and a version of MetaPost (written in C) that can handle larger quantities and fulfills some long standing wishes of the MetaPost development team.
All these projects report on a regular basis in (local) TeX usergroup journals and at TeX related conferences. Normally the most recent information can be acquired in the ConTeXt universe: mailing lists, source code, status documents and manuals.
The latest stable release is 0.77 which is the TeXlive 2013 version and the 0.78 beta will be available end of 2013 as a prelude to version 0.80 for TeXlive 2014. You can fetch the latest binaries for quite some platforms from The ConTeXt Garden or compile them from source yourself.