These are rez packages mainly authored for the Windows platform, but Linux and eventually Mac variants would be nice to have as well.
Rez is well suited for package management for VFX work, and a little bit of environment management if you use "suites". See rez's well-formulated docs for how it is designed and used if you haven't already!
As a developer I'd long searched for how to develop for DCC (digital content creation) apps while keeping my installation and user directories pristine. While I have used other systems working in VFX, rez really solves that problem elegantly. Of course, that's not the only problem it solves. It's also not the only solution, and I have yet to try similar tools such as spk and wiz.
Rez is used in some VFX/animation houses and has been for some time. Lately it has been designated as a potential candidate for being added to the ASWF. That would likely spread it's usage to other studios and definitely increase the manpower behind its development substantially. If you haven't given it a try yet I'd recommend it whole-heartedly.