I've been using @onlyME's Muscibox app for about 3 years, and the application keeps getting better and better with every update. This is definitely one of the better applications out there for IPS as far a features, and support goes. The support provided by onlyME is above and beyond anything I've come to expect from the marketplace. He listens to suggestions and works with me to find good solutions that are effective.
I highly recommend this application, or any application by this very talented programmer, as you will not only get quality, but incredibly fast and efficient support. You just can't go wrong working with @onlyME
After testing Collabs for a couple of days, I am really impressed with the breadth and scope of this app. Mind you, I'm still testing and figuring out what I can and can't do (specifically with reference to the relation between the Collab and the main site with the various apps). But once you get your Collabs (or Domains in my case) up and running, you can really get a sense of what you can do in terms of the granular permissions available for each domain. Sure, there are things I'd like to see which aren't there, and a few minor cosmetic issues, but that's why there are updates. Reading the support section, it's great to see someone so open to feedback from his clients as well.
I was going to give Collabs 4 stars for one reason: the lack of documentation. This is an app that could really benefit from some clear, straightforward documentation, even if it's just to explain the concepts behind it, e.g., the relationship of container categories to other containers and domains, the process of extracting content back to the main site, etc (especially where Pages is concerned). However, what bumped it back up to 5 stars was @Kevin Carwile's unflinching dedication to answering the questions his clients ask of him. Truly impressive, especially with a n00b like me who has lots of questions which likely have already been dealt with!
There are a lot of larger companies and corporations which could seriously take a page from Kevin's book re: the dedication to customer support and knowledge in the replies I get. I'm happy to support this product as Invision moves into 4.2 and beyond!