timeline navigation widget/plugin

If I’m not mistaken, you basically want a vertical timeline.

How about this?

https://www.ads-software.com/extend/plugins/wordpress-posts-timeline/

thanks dc_photo, but it’s not the timeline itself i’m interested in, it’s the navigation to the right of it.

I’ve never done anything of the sort, but if I were to have a go with custom code, I would first look into some combination of jQuery Accordian and wp_get_archives() in my sidebar template. I hope this points you in a good direction, good luck.