Latest released version (with sources), which is also available on CTAN.
The purpose of this TUG TeXnical Working Group (WG-94-07) is to develop and maintain a document that describes a standard TeX Directory Structure (TDS): a directory hierarchy for macros, fonts, and the other implementation-independent TeX system files. As a matter of practicality, we also suggests ways to incorporate the other TeX system files into a single structure. The TDS has been designed to work on all modern operating systems.
We hope that administrators and developers of both free and commercial TeX implementations will adopt this standard (most have, as of this writing).