The following was written in 2009, quite a long time before the existence of TiddlySpace. Things have changed since then, but the core principles in this document remain useful.
Because TiddlyWeb has tools for storing data and presenting that data in various forms over HTTP, it has some of the core features of a web application framework. However, since it (intentionally) is also missing some of the core features of a web application framework, a fair piece of cognitive dissonance can happen when the tool is approached as a web application framework (however if that's your thing, you may find TiddlyWeb Plugin Tutorial useful).
So it seems best to stay away from saying that TiddlyWeb is a web application framework, so as to manage expectations. The question remains, "What is it?"
One pathway to answering that question is to create tools with it and see what the commonalities are between those tools. A derivative of this approach is to create a killer app with TiddlyWeb: a something which demonstrates all the salient features and how to use them, both as a user and as a developer.
This approach seems to falter: The concepts in TiddlyWeb are sufficiently strange (I won't say unique, because they aren't that, they are common concepts, with their own spin) that in order to create a tool that uses them well you first need to either understand them in the abstract, or see some examples. Catch 22, especially if you are an examples oriented person.
@fnd and @cdent used to converse on this topic about daily, trying to come up with different strategies for answering it. One day it was suggested that instead of creating a new application, from scratch, that is cool and interesting because it uses TiddlyWeb, it might be better to find some application that could be made better through the addition or inclusion of TiddlyWeb.
It turns out this process has already started and by analyzing that process we might understand TiddlyWeb better.
The process has started with TiddlyWiki. TiddlyWiki is made better for a particular set of use cases by taking advantage of TiddlyWeb features. The fundamental experience of TiddlyWiki does not change: you've still got a wiki in an HTML file, with these things called tiddlers, some of which are special plugins that change behaviors.
- Centralization of content storage, storing at the level of the tiddler, with revisions, protection against editing conflicts and access control to read, write, create and delete; accessible from multiple locations on the network.
- A (hopefully) straightforward system of managing access control of tiddlers and making other kinds of groupings of tiddlers through the use of bags. Bags are collections of uniquely named Tiddlers.
- A system for composing functional collections of tiddlers selected from multiple bags using recipes. Recipes are list of bags paired with filters. Filters are rules which limit the tiddlers pulled from a bag when processing the recipe.
- Tools for viewing and manipulating tiddlers in different forms than those used in the wiki (e.g. JSON, Atom).
These four things together provide a multi-user environment for TiddlyWiki that allows multiple custom views of the same or similar content, depending on some piece of context. Different recipes can provide a different view on the same stuff, providing a different look and feel, different security handling, etc.
TiddlyWeb has many other features, but the above four are probably the key aspects which define its special sauce. When I evaluate a nascent TiddlyWeb tool for its tiddly-fitness the evaluation is done based on the extent to which the system takes advantage of and understands the above features.
These ideas should allow us to create some mental heuristics to use when approaching a TiddlyWeb project. If we have an existing project or use case that we intuit will be helped by using TiddlyWeb we can ask ourselves: 1) What aspects of this project will benefit from bags, recipes and filters? 2) How can we take advantage of different representations?
If, for some reason, we are planning to make a project from scratch, and have decided to use TiddlyWeb prior to really evaluating our use cases, then we can ask ourselves: 1) How can we best structure our data and UI to use recipes, bags and filters to provide flexible user experiences? 2) What representations can we present to allow other people to provide flexible user experiences?