What is the "standard" JQuery treeview that most people use? It seems the most popular plugin isn't supported anymore?

I don't know that there is a "standard" single solution for this. One I've used in the past that just got a major update is jsTree, it got a lot of improvements...it doesn't fit your "stable" requirement because it's in RC status, but that should change soon.

You can get more info on it here (it is large though, make sure it's not overkill for your needs)

There are certainly other options, but as I haven't used any of them (and we eventually went to a custom tree since our requirements were very light/specific)...I just can't give any first-hand experience information for the alternatives. I'll it for someone who's actually used them to give some insight.

Also, the jQuery UI Tree is coming, it's currently in the planning stages, you can track it's progress here: http://jqueryui.pbworks.com/Tree

For anyone looking for a "Checkbox Treeview", look no further: https://code.google.com/p/checkboxtree/

I stumbled upon this question when looking for a Checkbox Treeview so I thought I'd post a link - maybe helpful to others out there like myself!