TiddlyWiki is a fascinating project.
They describe it as:
[A] unique non-linear notebook for capturing, organising and sharing complex information.
Sounds like a cute little, low-tech piece of software. But then you dig into the documentation. Tiddlers are “[small] semantically meaningful units” of information. TiddlyWiki is a system for creating, storing these Tiddlers and model relationships between them. This lets you filter, aggregate and compose the information in various ways.
You can store the file locally and open it in your browser without having to install anything. You can share it over a network using something like Dropbox. Or you can have it on a server so you can access it online.