Recs.
Updated
A non-linear personal notebook used as a single HTML file in the browser or as a powerful Node.js application.
SpecsUpdate
Pros
Pro Active and helpful community typically answers questions within hours
The official support forum is at talk.tiddlywiki.org. It's frequented by a large number of knowledgeable TiddlyWiki enthusiasts. You rarely see a question go unanswered more than 2 or 3 days, and in most cases questions are answered within minutes. For harder questions, the developer himself frequently wades in to add information.
Pro Lightweight and very customizable
Variety of settings, and community themes & plugins, available from built-in marketplace (CPL library). Every community plugin is open-source which means you can learn from it and develop your own. Some plugin don't require programming knowledge (written using WikiText), and is very easy to learn.
Pro Progressive user level, from ease of use to programming your own plugins
Basic users can start with simple note-taking, progressively discover predefined features and existing plugins, then start using more fancy features (like filters, widgets, macros), in order to adapt their wiki to their needs.