There is ant http://ant.berlios.de/, but it is supposed to be saner form of TeX (in terms of source code, and easy of configuration) which was developed from scratch. The user interface is quite similar to TeX. I do not know much about the internal differences between Ant and TeX.
ANT have many major improvements. But as to the output pdf file of ANT, I cannot see much difference:(
River detection, which is done by ant, but not by TeX. Also since the computers now are more powerful, I think that doing page breaking on a global manner (or atleast by looking two three pages down, rather than just the current page), will make certain things (like long mathematical forumlas, and complex footnotes) appear nicely without a lot of manual tweaking. Agreed. River detection and global page break are very important for an advanced Typesetting system. I think control arbitrary streams on pages (available many advanced software, like InDesign) are also useful. I hope they will be in LuaTeX soon.