As Wikipedia grew in popularity, becoming the eighth most visited site on the Web, many companies decided to purchase and build wikis internally to help enable better communication, knowledge sharing, collaboration and project management between employees.

There are several free Web 2.0 offerings which help users who are new to wikis get their feet wet without installing software on a computer. We take a look at a four of them here:

1. Wiki: Google Sites (part of Google Apps)

Where it came from: Google Sites was built upon Google's acquisition of Jotspot, one of the companies that realized early on wikis had a future as a technology for the workplace.

Getting started: Signing up merely requires a Gmail account. When you sign into Gmail, click on the "More" tab and then "Sites" and you're into the app. You will be prompted to "create site" and you'll be able to decide rather quickly how you want to arrange things as they give you a few templates to choose from. A good starting off point is the web page view.

Ups: Have as many users as you want, and you can make the site publicly accessible if you wanted to take it beyond the corporate walls. Very easy editing tool that looks largely like what you'd use in your e-mail program, or a basic word processor. Like all the wikis mentioned here, you don't need to know how to write software code.

It's easy to embed video, links and other forms of media. There is great version control (so that if you don't like changes that were made, you can revert to an earlier form). Easy admin controls that allow you to make someone an administrator (who has the ability to create and terminate sites), collaborators (who can work within sites), and viewers (who can merely look at what's being done but can't edit). The ability to draw from Google Gadgets (a collection of widgets offered for iGoogle, such as a map or a stock ticker) is also nice.

Downs: No real mobile app to speak of. No offline mode. Though there are no ads to look at now, that could change as Google reserves the right to put ads on its consumer apps. Only 100 MB of storage per site. Pretty stingy considering Google's big server farms we always hear about.

2. Wiki: Socialtext

Where it comes from: Since its founding in 2002, Socialtext has been in the business of bringing social software such as wikis to the enterprise. They don't make their money off ads, so the free version of Socialtext (up to 5 users) is more or less a way for them to show businesses it is worth their time and money to sign up for their enterprise version that supports more users and contains more features.

Getting started: Go to Socialtext's customer login page and click on "get your own free Socialtext wiki."

Ups: Wikis do very well at providing users with context for the content their reading and consuming, and Socialtext is very good in this regard. You can embed content from within the confines of a social software environment (such as another wiki page or blog) as well as areas of the public Web. As an example, you can embed Google search results and RSS feeds rather easily by clicking on the "insert" drop down menu. It has good mobile access and the ability to take a wiki offline. Ability to tag content for easy discovery later on. If you're enamored enough by Socialtext's wiki, and want to expand your social software usage, the company also now gives you platform in which to create a blog.

Downs: While the editing tool allows for someone to post with no coding experience (just like Google Sites), it's not as pretty looking as the Google Sites text editor and has fewer options around font types. It's only free for only up to five users.

3. Wiki: Wikispaces

Where it comes from: Wikispaces is a three-year-old San Francisco start-up that focuses on hosting wikis for everything from businesses to schools.

Getting started: Pretty easy. Go to wikispaces.com and a light green sign up box can be found in the right corner.

Ups: The free version of Wikispaces doesn't have any limit for the amount of users and offers 2 GB of storage. The WYSIWYG (What You See is What You Get) editor is cool in that you can move it around the page to where you like it best. One elegant feature allows users to embed widgets (such as a YouTube video) very easily and have it appear nicely on the page. A "history" tab allows you not only to list previous versions but to compare them as well.

Downs: No mobile access and they've got to pay the bills, so they might serve up some ads along side the application.

4 Wiki: PB Wiki

Where it comes from: Since grabbing its first round of funding in 2006, PB Wiki has been hosting wikis for schools and companies such as AT&T, Citi and Cisco (see these examples on the company's home page).

Getting started: Go to pbwiki.com and click on the red button that says "create a wiki."

Ups: PB Wikis recently released a new version of their wiki that provides a good starting off point for someone with no wiki experience. It simply has two tabs at the top: "view," which would be like a read-only form, and "edit," to make changes/edits/deletions. You can backup your wiki offline if you're worried about something happening to it. The "Insert PlugIn" button in the text editor allows you to add content like the other leading free wikis. It includes the ability to add video (such as YouTube) and Google Gadgets. You can also upload views of key productivity apps, such as a calendar or spreadsheets. While most wikis rely on tagging and search as their primary ways of discovery (which it has), PB Wiki helps you bring the old fashioned folks into the fold with optional folders. Like Google Sites, it has a nice selection of fonts.

Downs: Only free for up to three users.