Zim is a graphical text editor used to maintain a collection of wiki pages. It is a "desktop wiki", which means it is a desktop application for personal use, not a website engine. The editor is a direct WYSIWYG editor, like a simple word processor.
Pages are stored in a folder structure using plain text files with wiki formatting, mixed with images etc. For collaboration various version control backends can be used (Bazaar, GIT, Mercurial).
Various plugins provide additional functionality, like a task list manager, an equation editor (using latex), a tray icon, and support for version control.