Tools

Metadata retriever

• Config Workbook - This tool extracts the metadata from any Salesforce Org in excel format. It covers FLS, Profiles, Page Layouts, Permission Set & their assignments as well as Apex details. Turns out this app has been removed from the AppExchange. I don't know why. :-( It's baaaack!!!
• Gorav Seth's blog post on parsing metadata with Open Refine.

Wikis

• Google Sites - (this!) The easiest way to make information accessible to people who need quick, up-to-date access.
• Confluence - Organize your work, create documents, and discuss everything in one place.

Video recording

• Jing - A computer service that lets you capture basic video, animation, and still images, and share them on the web.
• Camtasia - A powerful, yet easy-to-use screen recorder.

Other

• Screensteps - Helps you to create documentation that customers want to read.
• Salesforce Toolkit - tools that help you diagnose your org, compare environments, and activating and deactivating Salesforce components.