luatex

If they switch to luaTex nothing changes, because luaTeX is (intended to be) fully backwards compatible.

LuaTeX gives you hooks into the TeX system to customise certain aspects of the program's behaviour.

LuaTeX should do the same (being a drop-in replacement), the difference being that it can also use Lua scripts to control how the output is formatted (versus everything being written in TeX).

By the way, lualatex, from the LuaTeX project, behaves the same, although somewhat slower and infinitely scriptable in Lua.

I see a Java implementation, Windows implementations, LaTeX3 and LuaTeX are referred to as reimplemetations 'nearly from scratch', etc.

The pdfTeX / LuaTeX line is probably the most actively developed codebase.

So, luaTex is just an implementation of TeX written in Lua?

If you start writing your own packages, then luaTex becomes interesting.

LuaTex (actually quite easy, if you know the typesetting surroundings).

Oh, I forgot: LuaJitTex is a descendant of LuaTex that uses LuaJit to compile.

Recent distributions of LaTeX come with binaries luatex and lualatex.

However, some packages might not be adapted to LuaTeX, yet.

And then there is LuaTex: "LuaTeX is an extended version of pdfTeX using Lua as an embedded scripting language." See luatex.org.

You've managed to reply to me twice and in neither of those replies have you simply stated: "luatex is software that does x.

There have been a number of important packages that run on top of TeX, for example LaTeX and ConText and even enhanced implementations of TeX itself, like LuaTeX, pdftex, and xetex; however, only Knuth's TeX can be called "TeX".

Luatex is a rewrite that supports Unicode and TTF/OTF fonts and is scriptable in Lua.