I've always been a fan of the Easter egg, the meme version, where something or someone appears in one show or comic or book that exists in a totally different comic/book/show.. Examples include Warehouse13 & Eureka, Buffy & Angel, Golden Girls & Empty Nest & Nurses and Empty Nest & Full House.. Comic books do it as a standard (to sell more comics), I don't truly remember any crossovers done by any author, other than by themselves.

What I propose is to have you add your character, maybe a main character but possibly or preferrably a side character, who has the ability to travel to different worlds, either by science or fantasy, to a list, one you don't mind another author in adding to their world as a purely interesting visitor. They might interract with your main characters or maybe just provide a side note

"Across the street, a tall hooded man, dress in a brown cloak and with a top hat, stood watching the group intently, when one of them turned, he took up his suitcase and quickly walked away, he blended into the crowd so well, that Jane didn't notice him"

I use this between a few Gamesmastering friends via a google doc, but we thought it would work better if the list included thousands of possible visitors, and so people could pick or choose one, rather than having the same 4-5 guys..

As a contributor, you're free to use the list for your own crossover events and create quirky moments, that maybe your reader will spot, years later, having read both books and suddenly both authors will gain some new attention..

who knows.. if you include my character in your book, and you've provided us with a reference to it, I could write my story later with the reason WHY he was there.. building an even bigger set of crossover links!

I'll provide the google doc link for requesters, and award the first 20 (half decent or better) contributors with a simbi