TiddlyWiki is a wiki-modeled client-side single-page application written by Jeremy Ruston that is designed to be used as a personal notebook. It is a single self-contained HTML file that includes CSS and JavaScript code. When the user downloads it to their PC, TiddlyWiki can save the entered information by overwriting itself on the user's disk, at the user's request. Following TiddlyWiki conventions, users can make a new entry, called a tiddler, in their local copy of the TiddlyWiki file and save it for future reference. Existing tiddlers can also be modified or deleted in the same way. Because it runs under most browsers and requires no installation, it can be easily used as a portable personal wiki.