Wiki Tools

Fully Web Hosted, free/low cost

• Writeboard - One page wiki.
• Writely - Web word processor. Enables online storage of your documents, collaboration by invitation, export to multiple formats
• RallyPoint
• Zoho Writer - Online word processor with collaboration features.
• StikiPad
• EditMe
• Trac - Project tracking wiki.
• Wikispaces - Aimed at social groups.
• PBwiki
• SeedWiki
• Schtuff
• Instiki
• Wetpaint
• CourseForum

Download & Open Source

• MediaWiki - The software that powers Wikipedia.
• SnipSnap - product of the Frauhofer Institute Computer Architecture and Software Technology (FIRST) in Berlin, Germany.
• Swiki
• LauLima

Enterprise Wiki

• Atlassian Confluence
• JotSpot
• SocialText
• JotBox - Wiki appliance for large enterprises
• iUpload
• Stellent
• CustomerVision

Live Collaboration

• JotSpot Live
• SynchroEdit

Wiki Spreadsheet Tools

• JotSpot Spreadsheets
• Google Spreadsheets
• Zoho Sheet - Online alternative to traditional spreadsheet applications
  with powerful features like charting, collaboration & more.

WikiMatrix Side-by-side wiki software feature comparison