ViewPoint was CliffordAdams' initial (circa 2000) vision for a wiki supportive of multiple points of view, perspectives, etc. In 2005 CostinCozianu independently re-invented the idea as WikiChangeProposal. For more details, see the SisterSite page on MeatballWiki.
Contrast: ManaMana.
If indeed the differences are insufficient to make or break the acceptance of the concept by end users, then I would like to hear Clifford's comments on his and Costin's model of wiki. But since Costin is close to having a real product, that additional effort does merit a serious consideration by people interested in setting up wiki communities. -- DavidLiu