A wiki is nothing but a website that allows collaborative editing of its content and structure by its users. Wiki are social in nature. MediaWiki or DokuWiki are two excellent open sources web-based wiki software. For personal use, you might find desktop based wiki to take down notes and other stuff quickly. From the article:
If you want to get that wiki feeling on your desktop without dealing with all of that plumbing, you easily can. There are a number of solid lightweight wikis that can help you organize your information, keep track of your task, manage your notes, and more.
Let’s take a look at three of those lightweight, desktop wikis.