Wikis (the term comes from the word "quick" in Hawaiian) are collaboratively edited hypertext publications directly accessible by a web browser. They can contain multiple pages dedicated to different subjects. Wikipedia is by far the most famous wiki on the Internet, but it is not the first one historically. The first wiki software was the WikiWikiWeb (now archived), created by Ward Cunningham back in 1995.

Wikis differ from the traditional content management systems due to the fact that pages have no specific owner, and in most cases, everybody is free to create new pages and to edit existing pages.

External wiki

External or public wikis are wikis that are freely accessible on the Internet. They serve as resource centers or hubs for knowledge on different topics. Notable examples are Wikipedia and WikiTravel (both using MediaWiki open-source wiki software).

Internal wiki

Internal, or private, wikis are limited to a certain team within a company and sometimes to entire enterprises. They are used for managing internal knowledge base for a company. Organizations and enterprises often maintain their processes, procedures, guidelines, and policies in private wikis.

Personal wiki

Personal wiki differs from public and private wikis by their scope and intended audience. In many cases they also differ technically. In comparison to the standard wiki, personal wiki has a single owner and user - you. They contain information that is of your personal interest and, normally, they are not intended to be publicly accessible.

This changes the technical requirements to the wiki engine for personal wikis - you no longer need a public web server and in some cases any server at all! In these cases it is best to use desktop wiki software that works as standalone local and offline wiki software.

So a personal wiki is always a single user wiki. When it is installed on your own computer it is also a desktop wiki and a local wiki. And in most cases it is also an offline wiki since the data resides on your computer system and you need no Internet connection in order to access it. Some apps can be installed on a thumb drive or an USB stick. In that case you have a portable wiki software.

You can create a personal wiki for different purposes. The most popular uses of such wikis are:

• Empty your head - create an external brain for yourself. Write down everything that is keeping your mind busy.
• Note-taking - use it as a note taking app with a loose structure. Just create a new page for each idea that you have in your new personal wiki notebook.
• Personal knowledge base - do often forget how to do certain things? Write them down, so the next time you have a blueprint with the exact steps.
• Client manager - create your own customer relationship management system by writing down client details, meeting notes, and important dates.
• Project management - keep all the nifty details about your next project in one place.
• Research - collect your research notes and references in a single place.
• Free form database - wondering how to keep track of your collections? The personal wiki can be your friend here..

While public wikis need strong collaborative features and comprehensive page history, and revisions, personal wikis have different requirements. Ease of use and tools to organize pages are the top priority here.

• Ease of installation - no need to dwell on this one. Best personal wikis should not require installing additional software or a server.
• Text editor - traditional wikis often require writing pages in a special markup like Wikitext or Markdown. However, for a personal wiki, you should be looking for tools that offer visual text editing (also known as WYSIWYG - what you see is what you get). It makes writing easier and faster, because it is not prone to errors and you see your changes instantly.
• Rich text formatting - whether you prefer plain texts or beautifully formatted pages depends on your needs and preferences. That will determine how advanced the formatting features of the text editor should be. However, almost everybody needs two types of content to have a fully functioning wiki. Strong image support for visual representation of ideas, places, and people and tools for creating tables for structured data.
• Bi-directional linking or backlinks - we should be able to quickly see all connected pages and navigate between them easily.
• Full-text search - all wikis need a powerful search function for finding your information. If you are power user, look for engines that offer advanced search syntax, where you can specify in which parts of the page to search and what kind of pages to find.
• Page revisions - keeping track of changes to your pages is not as important as in a public wiki but could be helpful in some cases.
• Encryption - it is good to have some form of password-protection, if your wiki contains sensitive private information and confidential data.
• Portable wiki - your work may require that you travel a lot and use different computers. Then having your wiki on a USB drive can be a lifesaver.
• Table of contents - it is useful to have a list of all wiki pages for easier navigation. Some personal wikis also allow for having your pages in a hierarchy, not just in a flat list.
• Import - probably you already have much of the data for your personal wiki available on your computer in the form of documents, spreadsheets, and PDFs. In that case having strong import capabilities is a must for jump-starting your wiki.
• Offline wiki - this is strictly optional, depending on your preference, but in some cases you want your wiki to be independent of Internet access, especially if you are security conscious or on the go