I wrote and use daily <a href="http://onemodel.org" rel="nofollow">http://onemodel.org</a> (AGPL, uses postgres), for many reasons listed there :) . One way to think of its current state is a text-mode, easy-to-learn (i hope) infinite mind map of things, where I store <i>and can query</i> effectively everything: calendar, reminders, quasi-anki-like knowledge review, journal, automatic activity log, notes on subjects, very efficiently for the user.
(It also stores documents, but that is not very smooth compared to other document systems, nor is browser integration smooth at all.)<p>Edit: It also has a very basic security model (private, public, unspecified), and with that in mind, can export trees of notes as html or as outline documents (text), with or w/o indentation & numbering, which I've found very useful. And anything can be in as many places in the tree as is helpful. The export to simple html, I use to generate my 2 web sites.<p>(I plan to move it to Rust, and maybe sqlite, eventually, as well as add features like anki, internal code attached to entity classes for cheap internal customization/automation, etc, but have been slow lately.)<p>(Edit: it is currently only self-hosted by each user. Have considered doing hosting for other users, and might some day.)