Elsewhere in these FAQs, we learn that development of PDFTeX is “in essence” complete — no new facilities are being developed at the time of writing. The PDFTeX team has announced that they have frozen PDFTeX’s specification in its current state (version 1.40.11), and that nothing but bug corrections will be provided up to the time of the final release, PDFTeX 1.50.0. (The interpretation of the statement seems to allow sensible changes that are beyond any reasonable definition of bug…)
As PDFTeX development ran down, development of a new system, LuaTeX was started. Lua is a interpreter designed to be incorporated into other applications. LuaTeX consists of a TeX-like engine with a lua interpreter ‘embedded’ in it; the lua interpreter has access to many of the data structures used for typesetting, so that the programmer may also interpolate chunks of lua code into their (La)TeX macros, or as ‘call-backs’ for use when the TeX-like engine does certain operations.
This arrangement offers the prospect of a “semi-soft” typesetting engine: it will have its basic behaviour, but the user gets to redefine functionality if an idea occurs — there will be no need to persuade the world first, and then find a willing developer to work on the sources of of the distribution.
The LuaTeX project is (with monetary support from various sources) pursuing avenues that many of the other current projects have in their sights, notably Unicode character representations and support for OpenType fonts. The intention is to integrate the extensions pioneered by Aleph. Users may also care to view the LuaTeX documentation page or the LuaTeX WIKI
texlive (2013) holds version 0.76.0 of LuaTeX. This version demonstrates the “final functionality”, though the project remains a β-release. Functional stability was first declared for version 0.50.0, released near the end of December 2009.
CONTeXT ‘Mark 4’ can already make use of LuaTeX; much of its
code already appears in two forms — a TeX-based version
(mkii) and a ‘mkiv’ version (new functionality
typically only appears in ‘mkiv’ form), which uses
LuaTeX extensions (including lua scripting). LaTeX
packages that support its use are appearing (some of them providing
re-implementations of existing Context code).
LaTeX running over LuaTeX (commonly known as LuaLaTeX) is not an “official” entity (yet), but useful packages are appearing (i.e., the CTAN path macros/luatex/latex holds several items).
This answer last edited: 2013-05-21
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=luatex