LaTeX3
The expl3 (LaTeX3) Development Repository
...Some older reports from the early days of the project (mainly of historical interest) are available from the Comprehensive TeX Archive Network (CTAN) as ltx3pub. The repository contains development material for expl3. This includes not only code to be developed into the expl3 kernel, but also a variety of test, documentation and more experimental material. All of this code works on top of LaTeX2e.