Ajax sliders for content fragments. Fancy replacement for foot- and other notes.
Check out the Sliding Notes plug-in homepage for in-depth information about the plug-in.
The release announcements (see the links in the Changelog) provide in-depth information about the particular releases.
Version 1.6.5 is presumably the very last release in the 1st generation of Sliding Notes. Development of the next generation is taking over on a brand new shiny website.
The next generation of Sliding Notes is being rewritten from scratch, based on an entirely new concept that will enable cool features like linkability, skinnability, and more.
Naturally, it will be inevitable that some of the things will work differently than before, so users may have to adapt this or that (most probably CSS code).
You should connect with development for early access to information about upcoming changes and compatibility workarounds that may arise from them.