Tiddlywiki on isiklik viki ja mittelineaarne märkmik keeruka teabe korraldamiseks ja jagamiseks. See on avatud lähtekoodiga ühelehelise rakenduse wiki ühe HTML-faili kujul, mis sisaldab CSS-i, JavaScripti ja sisu. See on loodud nii, et see on lihtne kohandada ja ümber kujundada sõltuvalt rakendusest. See hõlbustab sisu uuesti kasutamist, jagades selle väikesteks tükkideks, mida nimetatakse Tiddlersiks.

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.