Wiggio looks pretty nice. But the disclaimers in their privacy policy would make me a little concerned about what company information I'd put up there.

To be fair, their policy isn't all that different than many online collaboration offerings.

What does bother me, however is the fact that they interface with various 3rd parties who pay Wiggio for access to its non-paying user base.

Wiggio is very careful to point out they have no control over their partner's actions. Nor does Wiggio require that any of these unidentified 3rd parties adhere to Wiggio's privacy policies. In fact, they wash their hands of anything their partners may get up to:

This privacy policy covers the use of cookies by Wiggio and does not cover the use of cookies or other tracking technologies by any of its advertisers.

Something about that would make me think twice. If I decided to go with a web-based solution, I'd feel safer if I were paying for the service. The Wiggio revenue stream is too dependent on entities other than it's actual users for me feel comfortable using it for business purposes.

This is not a wiki (no history, etc) but a very simple to use program that does what you want and you may already own.

If you have MS Office, see if you have OneNote available - it comes in some versions.  Set up a shared OneNote folder, put in a simple template.  Get each person to start OneNote and find the shared folder (only need to do that once).  If you can type in a Word document, you already know how to edit OneNote. I wouldn't bother buying it just for this, but if you already own it ...