DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Zim Wiki - Zim is a graphical text editor used to maintain a collection of wiki pages. Each page can contain links to other pages, simple formatting and images.
TiddlyWiki - a non-linear personal web notebook
Pepperminty Wiki - An entire wiki in a single PHP file. Intended for small - medium sized wikis.
VoodooPad - VoodooPad is a personal wiki developed for the Mac OS. It lets users create a personal wiki by giving them the ability to manage a network of pages right from the desktop.
Nuclino - Nuclino works like a collective brain, helping teams bring all their knowledge, docs, and projects together in one place. It's a modern, simple, and blazingly fast way to collaborate.