The ExperienceUI is an addition to NSIS that enables fully skinned user interfaces. The ExperienceUI was the first 3rd-party user interface for NSIS and remains the fastest and richest in features.
We're in the process of standardizing the ExperienceUI's development. It's not quite finished yet, so there may be broken links. We have a Mercurial repository up and have been committing some bug fixes to the current source tree based on ExperienceUI 1.11pre, the last public release.
ExperienceUI 1.3.2 is the current release, part of a transition to Linux kernel version numbering. It will be considered beta quality. We expect to move rapidly through the release cycle, with very few changes between releases, and a focus more on tuning for stability. ExperienceUI 1.4.0 will be the next stable release and it will be derived from the current codebase.
Documentation is the biggest issue right now. The ExperienceUI documentation will be transitioned to an online manual to ease updates. We are still deciding whether to use Enano or write static HTML. A hybrid may also be possible, depending on how everything gets organized.
The ExperienceUI is being resurrected from a longstanding (over 2 years) development stall, as it is needed for some Enano related subprojects. We are focusing primarily on stabilizing the current codebase and adding flexibility options. Features are pretty much frozen FWIW.