vim-librarian.vim by Robert Malko is a fork of Andrew Radev's simple_bookmarks.vim that allows sets of bookmarks to be restored. Like the original version, the core feature is named bookmark management, but the commands are now prefixed with
VL to keep it separate.
VOoM (vim.org: VOoM) by Vlad Irnov emulates a two-pane text outliner. It can work with fold markers with level numbers, but it can also handle various markup formats, including Markdown and vimoutliner.
:Voom will create an outline of the current buffer, and the results will be displayed in a separate window.