Here is one way to explain the difference:
Collaboration is people working together (often with a common goal) to build one thing (think wiki page with one understanding). Collective efforts are the aggregation of people's individual efforts, sometimes in the same service, but do not have common goal or common effort (del.icio.us page for a URL is the collective understanding of individuals tagging of that page for their own use.
For example, the upvoting of questions and answers here on StackExchange is an example of collective effort that is, to good approximation, not collaborative. The upvotes and downvotes are not coordinated between various members. The process results in a collective judgment on the issue of which answers (and questions) are the best. It is mostly an aggregate effect without (too) much mutual feedback. (Of course, in reality, there is some feedback—when an answer gets a lot of upvotes, it becomes more visible, which increases the chance that, other things being equal, even more people will see it and upvote it.) But ideally each vote is a result of an independent consideration on the part of each voting member.
On the other hand, when parents raise a child in a two-parent family, that is an example of collaboration. There is much coordination between the parents; each one is (ideally) aware of what the other has done, is doing, and will do, with the understanding that each action contributes to the common goal. Both parents have some say as far as what the other parent should do.
For a similar explanation which specifically concerns collective understanding vs. collaborative understanding, see here.