HTLS stands for Historical and Theological Lexicon of the Septuagint! You can find its site here, and get some impression for yourself, but it surely looks interesting!
Here is their own presentation: “This large-scale collective and interdisciplinary project will aim to produce a new research tool: a multi-volume dictionary giving an article of between 2 and 10 pages (around 500 articles in all) for each important word or word group of the Septuagint. Filling an important gap in the fields of ancient philology and religious studies, the dictionary will be based on original research of the highest scientific level.”
There is a solid group of scholars behind the project as presented on this site, there is a further description, and a page with lots of LXX related links. There is also a page for Contact, in which you can apply for access.