Lots of choices for social networking & collaboration tools. Those looking for replacements for Ning are probably most interested in the private/closed social networks that are free and hosted.
Directory of tools that do at least some of what Flash can do or that work with Flash--presentation tools, quiz tools, PowerPoint to Flash converters, ActionScript editors, etc. Most have free demos; not many open source options in this area.
Free tool for course authoring. Screen captures and PowerPoint imports are paid extras, but the basic tool is free. Might be nice for creating portfolio samples if you don't have access to Captivate or Articulate.
Open source Google Docs backup tool. It checks whether the Google Docs file already exists on your computer and if it's an older version and only downloads a backup copy if needed.
I was just trying to figure out how to get a news feed from Google today and was stumped. Google changed the interface and no longer provides a direct link, but you can manually create the feed.
You just have to manually rewrite the search URL, adding “<i>&output=rss</i>“.
Check website accessibility with a free tool from WebAIM. You can enter a URL, upload a file, or paste HTML code. There's also a Firefox toolbar that lets you check content that is password protected etc.