There are 2 potential future XWiki competitors I'm keeping an eye on right now. They're still in pre-production mode so it's unlikely we'll be competing against them in the short-term, but it's always interesting to see where the industry seems to be heading towards. They are:
PODIO
PROFERI SOFTWARE
Got invested in and pitched by Ben Horowitz. Looks like it's targeting business application and collaboration as well.
EDIT: AND HERE'S A THIRD ONE
ASANA
Was founded by a facebook co-founder. Tackling interesting challenges.
I'm however still circumspect about them. 2 other companies I thought to be promising and potential competitors never really materialized:
- http://www.wagn.org/ -> never met an actual implementation in real life
- http://dabbledb.com/ -> got bought by Twitter, service shut down
Now let's see whether those 2 prove me wrong :-)