The NTS project was established in 1992, to produce a typesetting system that's even better than TeX. The project is not simply enhancing TeX, for two reasons: first, that TeX itself has been frozen by Knuth (see the future of TeX), and second, even if they were allowed to develop the program, some members of the NTS team feel that TeX in its present form is simply unsuited to further development. While all those involved in the project are committed to TeX, they recognise that the end product may very well have little in common with TeX other than its philosophy.
The group's first product was nevertheless a set of extensions and enhancements to TeX, implemented through the standard medium of a change-file. The extended system is known e-TeX, and is 100textpercent compatible with TeX; furthermore, e-TeX can construct a format that is "TeX", with no extensions or enhancements present.
The most recent base source of e-TeX (i.e., the Web change file) is available on CTAN. Implementations of e-TeX are also distributed on the TeX Live CDROM, and with most other modern free TeX distributions.
The project has now produced a beta-version of TeX written (from scratch) in Java. Since it isn't TeX (it remains slightly incompatible in microscopic ways), it's known as NTS. As might be expected, this first re-implementation runs rather slowly, but its operation has been demonstrated in public, and the beta-release is available on CTAN.