I have collaborated on several projects in different ways, I think the first was collaboratively writing a poem with another member on writingforums.com. My latest is also with another member who has written a young adult's novel; an excellent plot, but the English requires considerable editing. Look out for 'Bagla's children', though there is some way to go yet.
On a more personal level I have helped others with their personal recollections, both in editing language and suggesting content formatting and direction.
Some ways I am getting old, original material is harder to think of, the other side of the coin is that I have experience. Other ways I am not, I am still open to considering all sorts of sensible, absurd and outlandish, ideas. That does not mean I will take them all on, but I will give an opinion.