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.