TiddlyWiki is a personal wiki and a non-linear notebook for organising and sharing complex information. It is an open-source single page application wiki in the form of a single HTML file that includes CSS, JavaScript, and the content. It is designed to be easy to customize and re-shape depending on application. It facilitates re-use of content by dividing it into small pieces called Tiddlers.

TiddlyWiki is designed for customization and to be shaped according to users’ specific needs, perhaps comparable to a high-end programming language. As such, it can be shaped into a wide and arbitrary range of special applications. Examples include niche note taking applications, to-do lists, presentations, collections, authoring tools, personal databases, recipe collections, etc.

Although there are many TiddlyWiki documents on the Web, the majority of TiddlyWikis reside on personal computers or in the cloud, or are exchanged over email, in a manner similar to word processing documents and spreadsheets. As a single HTML file, or saved as an HTA file in Microsoft Windows (allowing corporate IE lockdown to be bypassed), TiddlyWiki can be useful in corporate environments where red tape or IT resources might prevent the use of a wiki that requires a more complicated installation.