Actually, one pretty cool thing about the Kindles is, on older firmware revisions that came prior to Cloud Collections, it is actually possible to
add a collection to a collection, thus in effect creating nested collections!

Yes, I use this.
AFAIK, no other ereader out there supports this at all (and the Kindle only via a hack). You could do it with, say, Calibre Companion and hierarchical tags, but that is an android app.
Kindle Touch/PW1 or PW2 on fw5.4.0
Jailbreak is required, to use Collections Manager (kindlet).