No. I have only ever written on my own. I could never see myself writing with another person.
I've never worked with an artist, but for one NCIS Bigbang, as I mentioned in a previous question, an artist did do some artwork for the story. Also, when I had a couple of my fanfic novels/anthologies published in zine format, the co-editor did a few pieces of artwork to go with the stories.
28 – Have you ever collaborated with anyone else, whether writing together, or having an artist work on a piece about your fic?
29 – What is your current project or projects?
30 – Do you have a favourite fic you've written? What makes it your favourite? And don't forget to give us a link!